{O’ you who have true faith! Keep away from all sorts of conjecture since surely some types of conjecture may lead to sin. In addition, do not spy on and do not back-bite one another. Do any of you (who back-bite) love to eat the flesh of your dead brother? Rather, you detest this act, therefore have consciousness of Allah. Certainly Allah is the One who is Oft-Turning to you in Repentance, Merciful.}
In this verse, Allah (Glorified and Exalted is He) has made it incumbent upon the Muslim community to observe three ethical principles which are classified as the necessary rights (of Islam) and are the essentials of Islamic brotherhood and religious fellowship.
These three principles in summary are:
1. It is prohibited to have bad thoughts or be cynical of another Muslim.
2. A Muslim is not permitted to spy into the life of another Muslim.
3. It is forbidden to back-bite and talk bad about other Muslims behind their back.
Seeing as to how the principles that have been mentioned, form the primary ethical traits of Islam and play an important role in the improvement of society, and since we have beautiful and interesting explanations from the leaders of our religion in relation to these traits, it would be fitting to discuss each of these separately on their own with their independent analysis. At this point, we begin by discussing the first principle - spying on others.
Spying on others is a negative, psychological trait which can cause damage and injury to the character, respect, piety and spiritual purity of a person whom one is busy in thought about. A person who is pessimistic about others will forget about the thousands of good deeds and righteous actions that the person performs in his life and will only pay attention to those few vague, dark and murky actions of the person.
We all know that the life, wealth and honour of a Muslim is sacred and any sort of encroachment to these are prohibited in Islam. However in this verse, another form of injustice upon the rights of a Muslim has been alluded to and it is says that: “The respect, honour and character of every Muslim – even in our thoughts and imagination and in making judgements in our mind (about that Muslim) must also be respected and revered.” A Muslim is not permitted to cross the boundaries even in his mind in relation to the purity of another Muslim by harbouring bad thoughts or beliefs about him or her.
In the words of one of our present day Scholars, “The limits of security that Islam has brought forth for the Muslim society is not limited to just the life, wealth and character of another person. Rather, in addition to these three securities, there is also a fourth security which is required and that is the safety of being judged by others. By this, we mean that within one’s thoughts, one must not launch attacks or think bad and unpleasant thoughts about other people.
The respect and character of a Muslim, in addition to being practically adopted, is one that must also be protected in ones’ mind and thoughts.”
From the point of view of Islam, any sort of bad thoughts or misgiving in ones’ mind which would lead to tainting the character of another person is prohibited. Thus, we have been commanded that a society of people who have true faith will keep away from any sort of bad thoughts in relation to others.
In one of his most eloquent sayings in relation to the safety and security of a Muslim in relation to the four traits mentioned above, the Noble Prophet (blessings of Allah be upon him and his progeny) has stated:

إِنَّ اللٌّهَ حَرَّمَ عَلى الْمُسْلِمِ دَمَهُ وَ مٌالَهُ وَ عِرْضَهُ وَ أَنْ يَظُنَّ بِهِ سُوءَ الظَّنِ

“Certainly Allah has made sacred the blood, property and respect of a Muslim (from another Muslim) and he must not even entertain bad thoughts (about the other Muslim).”
If we see that the first three types of safety and sanctity that have been mentioned in the ahadith are enacted in the physical world and in the various global organizations, but the fourth – namely the safety of a person in relation to the thoughts that others entertain about him - is not acted upon except under the shadow of true faith in Allah (Glorified and Exalted is He), then it is because the limits of governance of the material (non-religious) world are limited to the apparent aspects of life only and preventing any sort of trespassing of the inner thoughts are out of the limits and boundaries of the powers mentioned.
Thus, it is only true faith in Allah (Glorified and Exalted is He) which can prevent a person from this sort of trespassing (through his thoughts), since a Muslim has firm conviction that Allah (Glorified and Exalted is He) sees all of the actions that he performs and is even aware of his inner thoughts.

The Dangers of Being Pessimistic About Others
1. The first result of distrusting others will return back to the person who himself possess this trait, since a person who does not trust others will never be able to imagine that others can do things without any (hidden) motive. Therefore, in addition to causing himself spiritual difficulties and putting his soul through troubles, one will lead a difficult life. Also, the burning and passion that are brought about through one’s imagination and thoughts will only increase the (mental) torture of a person.
2. Being pessimistic and not trusting other people also destroys the roots of friendship and harmony amongst people. The person who thinks bad about others will always imagine such people as being treacherous and will feel that their friendship is something that is not stable or is not built upon faithfulness (to one another). Thus, such people will be compelled to cut off relations with those around them and it is for this reason that the A’immah (peace be upon them all) have told us:

مَنْ غَلَبَ عَلَيْهِ سُوءُ الظَّنِّ لَمْ يَتْرُكْ بَيْنَهُ وَ بَيْنَ خَلِيلٍ صُلْحاً

“The person whose pessimism about others takes control over him will destroy any sort of peace or harmony that exists between himself and his friend.”
3. The person who is pessimistic and distrusts others will always be reclusive and will withdraw himself from others. Due to the fear and apprehension that he has for other people, he will never be able to be sociable with others and it is for this reason that we have been told in the ahadith:

مَنْ لَمْ يَحْسُنْ ظَنُّهُ إِسْتَوْحَشَ مِنْ كُلِّ أَحَدٍ

“A person who does not correct his thoughts about other people, will always be frightened of every single person.”
4. Being pessimistic and distrustful of others is a major calamity and will affect a person’s reason and ability to judge others, since this sickness is a type of disorder that affects the thought pattern and discernment of a person. Thus, he would never be able to judge a situation based upon his logical reasoning or by what reality is.
5. Pessimism is a sickness that is also contagious such that even those people that a pessimist sits and associates with, will fall into the filth of this negative trait.
6. Not only does pessimism and distrust affect the soul of a person, rather since there is a direct correlation between the body and the soul, the body too will remain un-healthy. In the words of the famous thinker of our time, Dr. Alexis Carol says, “Being pessimistic and always finding faults in things also takes away from the life span of a person since this harmful habit affects the nerves of the body known as the sympatic nerves and the internal glands as well. This can be the commencement of other physical disorders including affecting the limbs and organs of the body.”
7. Having bad thoughts about people without any reason will also drag ones’ spouse, employees, workers and helpers around the house into committing treachery and crimes. This is true since when the leader of the house or the husband continuously pries into the lives of others, then due to his associating thoughts to other people, an untrue picture or representation and despicable act will be made manifest to those around him and these untrue thoughts and feelings will get placed in the hearts of his close ones. In the words of some of the scholars, ‘The worker who is at the whims of the bad thoughts of his boss who is constantly thinking that his worker is stealing things from his house will slowly push his servant into actually stealing his property.’
Due to this, in the sacred teachings of Islam, pretending to be very zealous or passionate when the situation does not call for it, or to be extravagant in relation to one’s spouse has been highly discouraged. How many times has it occurred that an innocent, chaste person is pulled towards impurity and people who usually perform good deeds are tempted and encouraged to do bad deeds, just as Amir al-Mu’minin `Ali ibn Abi Talib (peace be upon him) has said: “I warn you about being overzealous and obsessive in improper occasions since unquestionably this act will tempt and encourage chaste women to go towards (spiritually) dirtied and fouled traits and would drag women who do not commit sin towards committing wicked deeds.”