Bowing down {ruku‘} is an essential pillar of prayer. Performing it in an excessive or inadequate manner, whether intentional or unintentional, renders the prayer invalid.
The word “rak‘ah” {circle} which is used in counting the cycles of prayer is derived from the word “ruku‘”.
The tribe of Thaqif requested that the Prophet (S) excuse them from performing ruku‘ and prostration {sujud} in prayer, saying: “Bending down for us is a shame.” This verse was revealed:

وَ إِذَا قِيلَ لَهُمُ ارْكَعُوا لا يَرْكَعُونَ

“When they are told, ‘Bow down,’ they do not bow down!”
Others bow and show reverence in front of human beings like themselves, but you have to bow down and show reverence solely to your Creator.
When the verse, “So celebrate the Name of your Lord, the All-supreme,” was revealed, the Prophet (S) ordered: “Show reverence to God while you are in ruku‘ and recite this dhikr {remembrance or glorification}:

سُبْحانَ رَبِّيَ الْعَظيمِ وَ بِحَمدهِ

Subhana rabbiya’l-‘azim wa bihamdih.
“Glory be to my Lord, the Great, and praise belongs to Him.”
We read in the traditions: “Ruku‘ is the sign of courtesy {adab} while the sujud is the symbol of nearness {qurb} to God. Once you do not perform the gesture of courtesy properly, you cannot be ready for the stage of nearness.”
Ruku‘ is the means of repentance {tawbah}, penitence and asking forgiveness in the presence of God:

فَاستَغْفَرَ رَبَّهُ وَ خَرَّ رَاكِعاً وَ أَنَاب‏

“Whereat he (David) pleaded with his Lord for forgiveness, and fell down bowing and repented.”

The effects of ruku‘
Imam al-Baqir (‘a) says: “Anyone who perfectly performs his ruku‘ perfectly will be safe from the horror of the grave.”
The more we bow down in humility to God, the more we shall have the power to confront the Satan and satanic ones. Imam as-Sadiq (‘a) says: “Long ruku‘ and sujud makes Iblis angry, saying, ‘Woe to me! With such quality of servitude, the people will no longer obey me.”
God says to the angels: “See my servants, how they express reverence to Me and they kneel down in front of Me. I shall also exalt them and give them honor and glory.”
Imam as-Sadiq (‘a) says: “A long ruku‘ and sujud have effects on the longevity of life.”

The etiquette of performing ruku‘
We read in the traditions that during ruku‘ the blessed back of the Messenger of Allah (S) would be so bent and so straight that if a drop of water was poured on his back, it would remain in the center of his back and not fall to either side.”
It is thus enjoined: “During ruku‘ stretch your neck as if to say: ‘I have accepted the faith even if I am beheaded in His way.”
Among the other etiquettes of performing ruku‘ is that men have to position their elbows outwardly like the wings of a bird and not to attach them to their flanks. We have to place the palms of our hands on our knees and spread our fingers. The feet must be aligned, neither one of them should be placed forward nor backward. Between the feet there must be the distance of about one hand span.
During ruku‘ one must look between the feet and after the recital of the dhikr for ruku‘, while still in the position of ruku‘ one must invoke blessings {salawah} upon Muhammad and his progeny (‘a). Of course, repetition of the dhikr for ruku‘ at least thrice has been recommended and is preferred.

The ruku‘ of the saints of God
Imam as-Sadiq (‘a) says: “Hadrat ‘Ali (‘a) would make his ruku‘ so long that his legs would perspire.”
Imam ‘Ali (‘a) himself thus says in the first sermon of Nahj al-Balaghah: “God has angels who are always in the state of ruku‘ and will never rise up {qiyam}.”
Of course, tiredness and hunger are not applicable to the angels. So, those who are gnostics and lovers of God and who perform such long ruku‘ persuade the angels to praise God. This is the state of the saints of God. Yet, what about us? The Prophet (S) was once sitting in the mosque when a certain man entered and stood in prayer, but his ruku‘ and sujud were defective and done very quickly. The Prophet (S) said: “He is like a crow that would peck and go. If he departs from this world with such a state of prayer, he will not have died under my religion.”

The history of sujud
After creating Adam (Adam) (‘a), God ordered the angels to prostrate before him. All of them prostrated except Iblis. On account of this defiance, God expelled him from His Presence.
The Qur’an mentions this episode repeatedly and we know that repetitions in the Qur’an are not without wisdom. It is as if it wants to say: “O man before whom all the angels prostrated! Why do you not prostrate before God, the Creator? O man! Iblis was expelled for refusing to prostrate before you. Once you refuse to prostrate before God, what can you expect?
“Iblis did not prostrate before you. He was saying: ‘I am superior to man.’ Can you afford to say: ‘I am superior to God’? You—who were once non-existent and once you came into the world, weakness and impotence enveloped your entire being, and in the end you shall also humbly depart from this world—how could you dare to be proud in front of the Creator of the universe?
At any rate, the first commandment of God after the creation of man was the command of prostration.

The importance of sujud
Sujud is the best position of man in the presence of God.
Sujud is the best way to attain nearness to God: “But prostrate and draw near {to Allah}!”
A sign of the loyal Companions of the Prophet (S) was that the effect of prostration could be seen on their foreheads: “Their mark is {visible} on their faces, from the effect of prostration.”
Sujud makes man harmonious and concordant with all of creation. This is because all creatures in heaven and on earth—from the stars to the plants—prostrate and are humble before God: “To Allah prostrates whatever is in the heavens and whatever is on the earth,” and “And the herb and the tree prostrate {to Allah}.”
Sujud means harmony with the angels of God. Hadrat ‘Ali (‘a) says: “There is no layer of the heavens without having therein a group of angels in the state of sujud.”
Sujud is the highest degree of obedience and servitude because man places on the earth the loftiest part of his body, i.e. his forehead, and expresses humility and impotence in the presence of the Omnipotent Authority.
Sujud is the most sublime station for the noblest men and women of the world. God commanded His Prophet (S) to prostrate, and that was not only during daytime but also during the night: “And worship Him for a watch of the night and glorify Him the night long.” And in addressing Hadrat Maryam (Saint Mary)—that pure and devoted woman—He says: “O Mary, be obedient to your Lord, and prostrate.”
Sujud comes after the ruku‘. It is a more perfect and higher stage than ruku‘, and brings the person praying to the peak of humility. As such, ruku‘ and sujud are usually mentioned together in the Qur’an. For example, “O you who have faith! Bow down and prostrate yourselves,” and “You see them bowing and prostrating {in worship}.”
Sujud is the symbol of faith in the divine signs: “Only those believe in Our signs who, when they are reminded of them, fall down in prostration.”
Nightly prostration is one of the signs of the righteous servants of God: “The servants of the All-beneficent are… those who spend the night with their Lord, prostrating and standing {in worship}.”
Sujud is the adornment of prayer. So, perform it properly. Imam as-Sadiq (‘a) says: “Whenever you perform prayer, perform the ruku‘ and sujud well as God will give seventy times the reward or even more.”
Sujud is the source of pride of God to the angels, and thus, it entails His favor such that in every sujud, one of man’s sins is forgiven and a great reward is recorded for him. Hadrat ‘Ali (‘a) said: “If man only knew what mercy envelopes him at the time of sujud, he would never raise up his head from that state.”
Sujud extinguishes the spirit of egoism and pride, and delivers man from vanity.
The Prophet (S) used to say: “On the Day of Resurrection, I will identify my ummah by the mark of prostration that they have on their foreheads.” That portion of the earth on which prostration was made will testify to the devotion of man on the Day of Resurrection and even in the world, a radiant point connect it to the heavens.
As in the case of ruku‘, long prostrations result in the permanence of favors and longevity.
Sujud is so important that God commands a great Prophet (S) such as Ibrahim (Abraham) (‘a), to cleanse Masjid al-Haram for those who perform the circumambulation {tawaf} of the Ka‘bah, ruku‘ and sujud.

The wisdom behind sujud
The Commander of the Faithful ‘Ali (‘a) was asked concerning the wisdom behind sujud. The Imam (‘a) said: “The first sujud means that I was dust in the beginning, and as I raise my head from sujud, it means that I came to the world from the dust. The second sujud means that I will again return to the soil, and as I raise my head from sujud, it means that on the Day of Resurrection I will rise up from the grave and be summoned.”
Imam as-Sadiq (‘a) says: “Since sujud is for God, it must therefore not be done on anything that is eaten or worn which draws the attention of materialists. Sujud must remind man of God, not the stomach, clothing and material things.”
We read in the hadith that the reason behind the prostration for forgetfulness {sujud sahwi} for unintentional excess and deficiencies (in the number of any essential pillar of the prayer) or misplaced utterance, standing and sitting is that Iblis distracted your attention and created disorder in your prayer.
Therefore, after prayer you perform two prostrations so as to rub his nose in the ground and to inform him that every time he creates disorder, you will again perform prostration before God.
Hadrat ‘Ali (‘a) said: “The external appearance {zahir} of the sujud is the placing of the forehead on the ground with sincerity and humility, but its esoteric essence {batin} is the detachment of the heart from all perishable things, attachment of the heart to the eternal abode, and relief from pride, fanaticism and all worldly attachments.

The etiquette of performing sujud
We shall point out some of the rules of etiquette of performing sujud as recorded in the traditions:
After ruku‘ in preparation for the performance of sujud, the hands must be placed first on the ground before the knees.
During the sujud the hands must be placed parallel to the ears. For men, the elbows must not be placed on the ground and must remain open on both sides like wings. Not only the forehead but also the nose must be placed on the ground. In between the two prostrations, the person praying must place his left foot under the right foot in such a manner that the weight of his body is on the left side because the left is the symbol of falsehood while the right is the symbol of truth.
During sujud the person praying, apart from the obligatory recital, has to send salawah, supplicate and weep out of fear of God. While rising from sujud, he has to recite takbir and during the recital of takbir, he has to raise both his hands.

The soil of Karbala’
Although sujud on any ground, nay on any clean stone and wood, is permissible and correct, the soil {turbah} of Imam al-Husayn has great merits. It is said that Imam as-Sadiq (‘a) would not prostrate on anything but the soil of Karbala’.
Sujud on the soil of Karbala’ tears away seven types of veils {hijabs} (that separate man from the Source of Light). It uplifts the prayer and makes it accepted. It also brings the person praying out of the abyss of material things, and acquaints him with jihad, blood and martyrdom.
Sujud on the soil of al-Husayn (‘a) means prayer accompanied by divine guardianship {wilayah}.
Sujud on the soil of al-Husayn (‘a) means prayer accompanied by martyrdom.
Sujud on the soil of al-Husayn (‘a) means commemorating the memory of the martyrs of Karbala’ who offered their blood for the sake of prayer and in the way of prayer.
Sujud on the soil of al-Husayn (‘a) means that every day is ‘Ashura’ and everyplace is Karbala’.
Sujud on the soil of al-Husayn (‘a) means that in the struggle against falsehood, one should offer his head and soul, but not subject himself to humiliation.
Yes, the shrine of al-Husayn (‘a) is one of the gardens of heaven and one of its gate.
Supplication under the dome of al-Husayn (‘a) is accepted and prayer in that place is beloved and accepted.
If the beads of a rosary {tasbih} made from the soil of Karbala’ are rotated in the hands, there shall be the reward of reciting “subhan Allah” {glory be to Allah} for the owner even if he is silent. If he does dhikr {the remembrance of God} and uses the rosary, there shall be 70 times the reward for each dhikr.
The importance of Karbala’ as mentioned in the traditions is not concealed so as for it to encompass so far as four miles away from the shrine of Imam al-Husayn (‘a).

Prostration of thanks {sujud shukr}
Prostration is not exclusive to prayer. In fact, it is also discussed in other areas and it is even obligatory sometimes such as after the recital of one of the verses for which prostration is obligatory.
One of the ways of expressing gratitude is the prostration of thanks {sujud shukr} which is highly recommended.
Sujud shukr means giving thanks for the incessant divine blessings which have been showered upon us and our family.
Imam as-Sadiq (‘a) says: “Whenever you remember a blessing, place your forehead on the ground as a token of thanks and if you see that the people are looking at you, as a respect for that favor, bend a little bit.”
The Holy Prophet (S) was seen dismounting a camel. He performed prostration five times and said: “Jibra’il came down to me and gave me five types of insight, and for every insight I made sajdah.”
Hadrat ‘Ali (‘a) sometimes would faint while performing sujud shukr and it has been narrated from the Imam of the Time (‘a) that the most necessary of the recommended acts {sunnah} is sujud shukr.
During the sujud shukr any dhikr or supplication is permissible, but the recital of “shukran lillah” {thanks to Allah} and “al-hamdulillah” {all praise belongs to Allah}, and remembrance of the great blessing of the guardianship {wilayah} of the Ahl al-Bayt (‘a) are recommended. God said: “The reward of the person who performs sujud shukr is that I also give thanks to him.”
Although there is a specific time and place for sujud shukr, the best time nevertheless is after every prayer as a supplement to the prayer.

The blessings of sujud shukr
Many blessings and benefits of sujud shukr have been mentioned in the traditions. We shall briefly state some of them below: If there is deficiency in prayer which is not removed through the recommended and optional prayers, sujud shukr will compensate for it. It entails the pleasure of God and removes the distance between man and God. Supplication during the sujud shukr is recommended and has the reward of ten salawats and the removal of ten major sins.
Concerning the station and status of sujud shukr, it is enough to say that God would be proud of it and express this pride to the angels.

The prostrations of the saints of God
Imam as-Sadiq (‘a) says: “The reason behind Ibrahim’s (‘a) attainment of the station of Friend of Allah {khalilullahi} was his many prostrations on the ground.
On the night when Hadrat ‘Ali (‘a) was supposed to sleep on the bed of the Holy Prophet (S) in order to protect him from the swords of his enemies, he asked the Messenger of Allah (S): “If I do so, will your life be safe from danger?” When the Prophet (S) gave an affirmative reply, Hadrat ‘Ali (‘a) smiled and performed sujud shukr as a gesture of gratitude for this opportunity.
When the head of Abu Jahl, leader of the polytheists, was brought to the Prophet (S), he performed sujud shukr.
Imam as-Sajjad (‘a) would perform sujud shukr as an expression of thanks. Whenever a calamity was taken away from him or he initiated the reconciliation between two Muslims, he would make sujud shukr. His sujud was so long that he would perspire profusely.

Some points
1. The place of prostration is so important in that we thus read in the traditions: “After prayer, touch the place of prostration with your hand and apply it to your face and body in order to remain safe from diseases, plagues and unpleasant things.”
2. Try not to forget sujud shukr after the maghrib {dusk} prayer as the supplication after it is accepted.
Imam as-Sadiq (‘a) said: “Anyone who performs prostration between the adhan and iqamah and thus says while in prostration, “I do prostrate before You humbly, submissively and meekly,” God will place love for him in the hearts of the believers and fear of him in the hearts of the hypocrites {munafiqin}.
3. Prostration is solely for God and it is not permissible to prostrate before anyone including the Prophet of Allah (S), let alone in front of the graves of the Imams (‘a) and their descendants {imamzadehs}, in front of which some people do prostrate as an expression of respect.
When a group of Muslims migrated to Abyssinia, the infidels of Mecca dispatched a delegation to King Negus in order for him not to accommodate the Muslims in his country and thus expel them. In accordance with the customs at that time, the representative of the Quraysh prostrated before the Negus (king of Abyssinia). On the contrary, the Muslim representative, Ja‘far, the brother of Hadrat ‘Ali (‘a), did not prostrate, saying: “We do not prostrate to anybody except God.”
The prostration of Hadrat Ya‘qub (Jacob) (‘a) and his sons to Hadrat Yusuf (Joseph) (‘a) was also not for Yusuf but for God as a token of gratitude for the blessing of reunion with Yusuf: “And they fell down prostrate before him.”