The noble Shaykh Ja’far ibn Qawlawayh al-Qummi has reported through a considerable chain of authority that Abu-Hamzah al-Thumali reported Imam al-Sadiq (‘a) as saying:
If you intend to visit the tomb of al-’Abbas ibn ‘Ali (‘a) that lies on the bank of the River Euphrates opposite to al-Ha’ir, you should stop at the gate of the shed (precinct) and say these words:

سَلامُ اللّٰهِ وَ سَلامُ مَلائِكَتِهِ الْمُقَرَّبِينَ وَ اَنْبِيَائِهِ الْمُرْسَلِينَ وَ عِبَادِهِ الصَّالِحِينَ وَ جَمِيعِ الشُّهَدَاءِ وَ الصِّدِّيقِينَ [وَ] الزَّاكِيَاتُ الطَّيِّبَاتُ فِيمَا تَغْتَدِي وَ تَرُوحُ عَلَيْكَ يَا ابْنَ اَمِيرِ الْمُؤْمِنِينَ اَشْهَدُ لَكَ بِالتَّسْلِيمِ وَ التَّصْدِيقِ وَ الْوَفَاءِ وَ النَّصِيحَةِ لِخَلَفِ النَّبِيِّ صَلَّى اللّٰهُ عَلَيْهِ وَ آلِهِ الْمُرْسَلِ وَ السِّبْطِ الْمُنْتَجَبِ وَ الدَّلِيلِ الْعَالِمِ وَ الْوَصِيِّ الْمُبَلِّغِ وَ الْمَظْلُومِ الْمُهْتَضَمِ فَجَزَاكَ اللّٰهُ عَنْ رَسُولِهِ وَ عَنْ اَمِيرِ الْمُؤْمِنِينَ وَ عَنِ الْحَسَنِ وَ الْحُسَيْنِ صَلَوَاتُ اللّٰهِ عَلَيْهِمْ اَفْضَلَ الْجَزَاءِ بِمَا صَبَرْتَ، وَ احْتَسَبْتَ وَ اَعَنْتَ فَنِعْمَ عُقْبَى الدَّارِ لَعَنَ اللّٰهُ مَنْ قَتَلَكَ وَ لَعَنَ اللّٰهُ مَنْ جَهِلَ حَقَّكَ وَ اسْتَخَفَّ بِحُرْمَتِكَ وَ لَعَنَ اللّٰهُ مَنْ حَالَ بَيْنَكَ وَ بَيْنَ مَاءِ الْفُرَاتِ اَشْهَدُ اَنَّكَ قُتِلْتَ مَظْلُوما وَ اَنَّ اللّٰهَ مُنْجِزٌ لَكُمْ مَا وَعَدَكُمْ جِئْتُكَ يَا ابْنَ اَمِيرِ الْمُؤْمِنِينَ وَافِدا اِلَيْكُمْ وَ قَلْبِي مُسَلِّمٌ لَكُمْ وَ تَابِعٌ وَ اَنَا لَكُمْ تَابِعٌ وَ نُصْرَتِي لَكُمْ مُعَدَّةٌ حَتَّى يَحْكُمَ اللّٰهُ وَ هُوَ خَيْرُ الْحَاكِمِينَ فَمَعَكُمْ مَعَكُمْ لا مَعَ عَدُوِّكُمْ اِنِّي بِكُمْ وَ بِاِيَابِكُمْ [وَ بِآبَائِكُمْ‏] مِنَ الْمُؤْمِنِينَ وَ بِمَنْ خَالَفَكُمْ وَ قَتَلَكُمْ مِنَ الْكَافِرِينَ قَتَلَ اللّٰهُ اُمَّةً قَتَلَتْكُمْ بِالْاَيْدِي وَ الْاَلْسُنِ.

You should then enter, throw yourself on the tomb, and say the following words:

السَّلامُ عَلَيْكَ اَيُّهَا الْعَبْدُ الصَّالِحُ الْمُطِيعُ لِلَّهِ وَ لِرَسُولِهِ وَ لِاَمِيرِ الْمُؤْمِنِينَ وَ الْحَسَنِ وَ الْحُسَيْنِ صَلَّى اللّٰهُ عَلَيْهِمْ وَ سَلَّمَ السَّلامُ عَلَيْكَ وَ رَحْمَةُ اللّٰهِ وَ بَرَكَاتُهُ وَ مَغْفِرَتُهُ وَ رِضْوَانُهُ وَ عَلَى رُوحِكَ وَ بَدَنِكَ اَشْهَدُ وَ اُشْهِدُ اللّٰهَ اَنَّكَ مَضَيْتَ عَلَى مَا مَضَى بِهِ الْبَدْرِيُّونَ وَ الْمُجَاهِدُونَ فِي سَبِيلِ اللّٰهِ الْمُنَاصِحُونَ لَهُ فِي جِهَادِ اَعْدَائِهِ الْمُبَالِغُونَ فِي نُصْرَةِ اَوْلِيَائِهِ الذَّابُّونَ عَنْ اَحِبَّائِهِ فَجَزَاكَ اللّٰهُ اَفْضَلَ الْجَزَاءِ وَ اَكْثَرَ الْجَزَاءِ وَ اَوْفَرَ الْجَزَاءِ وَ اَوْفَى جَزَاءِ اَحَدٍ مِمَّنْ وَفَى بِبَيْعَتِهِ وَ اسْتَجَابَ لَهُ دَعْوَتَهُ وَ اَطَاعَ وُلاةَ اَمْرِهِ، اَشْهَدُ اَنَّكَ قَدْ بَالَغْتَ فِي النَّصِيحَةِ وَ اَعْطَيْتَ غَايَةَ الْمَجْهُودِ فَبَعَثَكَ اللّٰهُ فِي الشُّهَدَاءِ وَ جَعَلَ رُوحَكَ مَعَ اَرْوَاحِ السُّعَدَاءِ وَ اَعْطَاكَ مِنْ جِنَانِهِ اَفْسَحَهَا مَنْزِلا وَ اَفْضَلَهَا غُرَفا وَ رَفَعَ ذِكْرَكَ فِي عِلِّيِّينَ [فِي الْعَالَمِينَ‏] وَ حَشَرَكَ مَعَ النَّبِيِّينَ وَ الصِّدِّيقِينَ وَ الشُّهَدَاءِ وَ الصَّالِحِينَ وَ حَسُنَ اُولَئِكَ رَفِيقا اَشْهَدُ اَنَّكَ لَمْ تَهِنْ وَ لَمْ تَنْكُلْ وَ اَنَّكَ مَضَيْتَ عَلَى بَصِيرَةٍ مِنْ اَمْرِكَ مُقْتَدِيا بِالصَّالِحِينَ وَ مُتَّبِعا لِلنَّبِيِّينَ فَجَمَعَ اللّٰهُ بَيْنَنَا وَ بَيْنَكَ وَ بَيْنَ رَسُولِهِ وَ اَوْلِيَائِهِ فِي مَنَازِلِ الْمُخْبِتِينَ فَاِنَّهُ اَرْحَمُ الرَّاحِمِينَ.

Translation:
Greetings of Allah, and greetings of His favourite angels, His commissioned Prophets, His pious servants, all martyrs, and truthfuls, and also true blessings, giving you joy and confidence, be on you, O the son of the Ameer ul Moomineen. I bear witness that you resigned yourself to the will of Allah. Sincerely accepted as true, faithfully kept your promise, showed yourself as a reliable friend, with regard to the grandson of the Prophet, (blessings of Allah be on him and on his children), he (Husayn) was his (Prophet’s) chosen grandson, the sagacious guide, the successor who promoted the religion  the wrongfully oppressed, so Allah rewarded you  on behalf of His Messenger, Ameer ul Moomineen, Hasan and Husayn, (blessings of Allah be on them), the bet recompense that your resignation, thoughtfulness, and support (to Allah’s religion) have earned for you. How excellent is the reward available in the life eternal ! Curse of Allah be on those who killed you, curse of Allah be on those who ignored your rights; gave no importance to your sanctity; curse of Allah be on those who stood between you and the river of Furaat. I bear witness that you were wrongfully killed. Verily Allah has fulfilled the promise He made with you. I am here, O the son of the Ameer ul Momineen  to present myself before you. I put faith in you, and I follow you, I am your obedient disciple, I am always ready to serve you, till Allah summons me, He is the Bet of all who direct (others) to do something. I am on your side, in your group, not among your enemies, I believe in you, and I am sure that (in the promised days) you all shall return; those who opposed you and killed you were the infidels; may Allah destroy those who gave the orders to kill you and those who carried it out.

You should then enter, throw yourself on the tomb, and say the following words:

Peace be on you, O the pious obedient servant of Allah, His Messenger, Ameerul Moominee, Husan and Husayn, blessings and greetings of Allah be on them. Peace be on you, mercy and blessings of Allah be on you; His protection and His patronage be for you, also on your body and soul. I bear witness and invoke Allah to be a witness that, verily, you lived and died as the warriors of Badr and the soldiers of Allah, in the cause of Allah, faithfully served Him in the battlefield against His enemies, did your best to support His intimate friends, and defend His beloved favourites; so, may Allah, reward you the best reward, continuous, exemplary and conclusive, which He gives to those who uphold the oath of loyalty, give answer to His call, and obey His command. I bear witness that, verily, you indeed served the cause 9of Allah), and made utmost efforts to pursue its purpose. Allah, therefore , has included you among the martyrs, and let your soul rest in peace with the souls of the fortunate, awarded you a spacious space in His Paradise, in the seventh Heaven, paid tribute to you by making mention of your name in the highest circle, chosen you to move in the company of the Prophets, the truthfuls, the martyrs and the pious, and those are the best companions. I bean witness that, verily, you did not lag behind, did not turn away the face; verily, you were fully aware of the truth at the time of leaving this world, following in the pious infallibles’ and the Prophets’ footsteps, so, may Allah assemble us together (His Messenger, His representatives, you and us), all those who have surrendered to Allah. Verily, He is the most Merciful

 

It is expedient to say this form of ziyarah while standing behind the holy tomb and facing the kiblah direction, as is also advised by Shaykh al-Tusi in his book of Tahdhib al-Ahkam.
You may then enter, throw yourself on the tomb, and say the following words while facing the kiblah direction:

السّلام عليك ايّها العبد الصّالح

 

According to the previously mentioned narration, the ziyarah of al-’Abbas ends here. But Sayyid Ibn Tawus and Shaykh al-Mufid, as well as other scholars, have added the following:
You may then turn to the side of the head and offer a two-unit prayer. Afterwards, you may offer prayers as many as you wish. You may also supplicate Almighty Allah earnestly. After these prayers, you may say the following supplicatory prayer:

اللّٰهُمَّ صَلِّ عَلَى مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ لا تَدَعْ لِي فِي هَذَا الْمَكَانِ الْمُكَرَّمِ وَ الْمَشْهَدِ الْمُعَظَّمِ ذَنْبا اِلا غَفَرْتَهُ وَ لا هَمّا اِلا فَرَّجْتَهُ وَ لا مَرَضا اِلا شَفَيْتَهُ وَ لا عَيْبا اِلا سَتَرْتَهُ وَ لا رِزْقا اِلا بَسَطْتَهُ وَ لا خَوْفا اِلا آمَنْتَهُ وَ لا شَمْلا اِلا جَمَعْتَهُ وَ لا غَائِبا اِلا حَفِظْتَهُ وَ اَدْنَيْتَهُ وَ لا حَاجَةً مِنْ حَوَائِجِ الدُّنْيَا وَ الْآخِرَةِ لَكَ فِيهَا رِضًى وَ لِي فِيهَا صَلاحٌ اِلا قَضَيْتَهَا يَا اَرْحَمَ الرَّاحِمِينَ.

You may then return to the tomb, stop at the side of the legs, and say the following words:

السَّلامُ عَلَيْكَ يَا اَبَا الْفَضْلِ الْعَبَّاسَ ابْنَ اَمِيرِ الْمُؤْمِنِينَ السَّلامُ عَلَيْكَ يَا ابْنَ سَيِّدِ الْوَصِيِّينَ السَّلامُ عَلَيْكَ يَا ابْنَ اَوَّلِ الْقَوْمِ اِسْلاما وَ اَقْدَمِهِمْ اِيمَانا وَ اَقْوَمِهِمْ بِدِينِ اللّٰهِ وَ اَحْوَطِهِمْ عَلَى الْاِسْلامِ اَشْهَدُ لَقَدْ نَصَحْتَ لِلَّهِ وَ لِرَسُولِهِ وَ لِاَخِيكَ فَنِعْمَ الْاَخُ الْمُوَاسِي فَلَعَنَ اللّٰهُ اُمَّةً قَتَلَتْكَ وَ لَعَنَ اللّٰهُ اُمَّةً ظَلَمَتْكَ وَ لَعَنَ اللّٰهُ اُمَّةً اسْتَحَلَّتْ مِنْكَ الْمَحَارِمَ وَ انْتَهَكَتْ حُرْمَةَ الْاِسْلامِ فَنِعْمَ الصَّابِرُ الْمُجَاهِدُ الْمُحَامِي النَّاصِرُ وَ الْاَخُ الدَّافِعُ عَنْ اَخِيهِ ، الْمُجِيبُ اِلَى طَاعَةِ رَبِّهِ الرَّاغِبُ فِيمَا زَهِدَ فِيهِ غَيْرُهُ مِنَ الثَّوَابِ الْجَزِيلِ وَ الثَّنَاءِ الْجَمِيلِ وَ اَلْحَقَكَ [فَاَلْحَقَكَ‏] اللّٰهُ بِدَرَجَةِ آبَائِكَ فِي جَنَّاتِ النَّعِيمِ اللّٰهُمَّ اِنِّي تَعَرَّضْتُ لِزِيَارَةِ اَوْلِيَائِكَ رَغْبَةً فِي ثَوَابِكَ وَ رَجَاءً لِمَغْفِرَتِكَ وَ جَزِيلِ اِحْسَانِكَ فَاَسْاَلُكَ اَنْ تُصَلِّيَ عَلَى مُحَمَّدٍ وَ آلِهِ الطَّاهِرِينَ وَ اَنْ تَجْعَلَ رِزْقِي بِهِمْ دَارّا وَ عَيْشِي بِهِمْ قَارّا وَ زِيَارَتِي بِهِمْ مَقْبُولَةً وَ حَيَاتِي بِهِمْ طَيِّبَةً وَ اَدْرِجْنِي اِدْرَاجَ الْمُكْرَمِينَ وَ اجْعَلْنِي مِمَّنْ يَنْقَلِبُ مِنْ زِيَارَةِ مَشَاهِدِ اَحِبَّائِكَ مُفْلِحا مُنْجِحا قَدِ اسْتَوْجَبَ غُفْرَانَ الذُّنُوبِ وَ سَتْرَ الْعُيُوبِ وَ كَشْفَ الْكُرُوبِ اِنَّكَ اَهْلُ التَّقْوَى وَ اَهْلُ الْمَغْفِرَةِ.

If you intend to take leave, you may approach the holy tomb and say the following words, which has been reported from Abu-Hamzah al-Thumali and have been mentioned by other scholars:

اَسْتَوْدِعُكَ اللّٰهَ وَ اَسْتَرْعِيكَ وَ اَقْرَاُ عَلَيْكَ السَّلامَ آمَنَّا بِاللّٰهِ وَ بِرَسُولِهِ وَ بِكِتَابِهِ وَ بِمَا جَاءَ بِهِ مِنْ عِنْدِ اللّٰهِ اللّٰهُمَّ فَاكْتُبْنَا مَعَ الشَّاهِدِينَ اللّٰهُمَّ لا تَجْعَلْهُ آخِرَ الْعَهْدِ مِنْ زِيَارَتِي قَبْرَ ابْنِ اَخِي رَسُولِكَ صَلَّى اللّٰهُ عَلَيْهِ وَ آلِهِ وَ ارْزُقْنِي زِيَارَتَهُ اَبَدا مَا اَبْقَيْتَنِي وَ احْشُرْنِي مَعَهُ وَ مَعَ آبَائِهِ فِي الْجِنَانِ وَ عَرِّفْ بَيْنِي وَ بَيْنَهُ وَ بَيْنَ رَسُولِكَ وَ اَوْلِيَائِكَ اللّٰهُمَّ صَلِّ عَلَى مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ تَوَفَّنِي عَلَى الْاِيمَانِ بِكَ وَ التَّصْدِيقِ بِرَسُولِكَ وَ الْوِلايَةِ لِعَلِيِّ بْنِ اَبِي طَالِبٍ وَ الْاَئِمَّةِ مِنْ وُلْدِهِ عَلَيْهِمُ السَّلامُ وَ الْبَرَاءَةِ مِنْ عَدُوِّهِمْ فَاِنِّي قَدْ رَضِيتُ يَا رَبِّي بِذَلِكَ وَ صَلَّى اللّٰهُ عَلَى مُحَمَّدٍ وَ آلِ مُحَمَّدٍ.

 

You may then pray Almighty Allah for yourself, your parents, your brethren-in-faith, and for Muslims. You may choose any statement of supplication you like.

STATURE AND POSITION OF AL ABBAS
Imam al-Sajjad, peace and blessings of Allah be upon him, is reported to have said, “May Allah have mercy upon al-’Abbas. He preferred his brother to himself and sacrificed himself for him until his two hands were severed. So, Almighty Allah shall give him as compensation two wings to fly with the angels in Paradise in the same way as He shall do to Ja’far ibn Abi-Talib. Verily, al-’Abbas shall enjoy such a supreme position with Almighty Allah due to which all martyrs will hope to have its like on the Resurrection Day.”
It has been also reported that al-’Abbas, peace be upon him, was thirty-four years old when he was martyred. His mother, Ummu’l-Banin, used to go out to the al-Baqi’ Cemetery to elegize, weep, and mourn for al-’Abbas and his brothers. Whoever passed be her would not be able to stop weeping for her mournful style.
Actually, it is not strange to find a loyalist (to the Ahl al-Bayt) weeping for al-’Abbas when he listened to the mournful words of Lady Ummu’l-Banin, because even Marwan ibn al-Hakam, the bitterest enemy of the Ahl al-Bayt, could not help weeping when he heard the mournful words of this lady.
Elegizing al-’Abbas and her other sons, Ummu’l-Banin composed the following poetic verses:

يَا مَنْ رَاَى الْعَبَّاسَ كَرَّ عَلَى جَمَاهِيرِ النَّقَدِوَ وَرَاهُ مِنْ اَبْنَاءِ حَيْدَرَ كُلُّ لَيْثٍ ذِي لَبَدٍ
اُنْبِئْتُ اَنَّ ابْنِي اُصِيبَ بِرَأْسِهِ مَقْطُوعَ يَدٍوَيْلِي عَلَى شِبْلِي اَمَالَ بِرَأْسِهِ ضَرْبُ الْعَمَدِ
لَوْ كَانَ سَيْفُكَ فِي يَدِيْكَلَمَا دَنَا مِنْهُ اَحَدٌ

She also composed the following verses:

لا تَدْعُوِنِّي وَيْكِ اُمَّ الْبَنِينَتُذَكِّرِينِي بِلِيُوثِ الْعَرِينِ
كَانَتْ بَنُونَ لِي اُدْعَى بِهِمْوَ الْيَوْمَ اَصْبَحْتُ وَ لا مِنْ بَنِينَ
اَرْبَعَةٌ مِثْلُ نُسُورِ الرُّبَىقَدْ وَاصَلُوا الْمَوْتَ بِقَطْعِ الْوَتِينِ
تَنَازَعَ الْخِرْصَانُ اَشْلاءَهُمْفَكُلُّهُمْ اَمْسَى صَرِيعا طَعِينَ
يَا لَيْتَ شِعْرِي اَ كَمَا اَخْبَرُوابِاَنَّ عَبَّاسا قَطِيعُ الْيَمِين