Avoiding Suspicion

"O you who have believed, avoid much [negative] assumptions. Indeed, some assumptions is sin. And do not spy or backbite each other. Would you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful."

(Qur'an: Surah al-Hujurat [The Dwellings] 49, verse 12)

This verse Allah SWT is teaching us about the consequences for such actions and also the right morals and social etiquette.

There are good assumptions and bad assumptions [suspicion]. Here are some types of assumptions:

Mandatory

It is mandatory upon a Muslim to have positive, good thoughts about Allah.

Recommended

To think positively about a righteous Muslim is recommended.

Forbidden

It is prohibited to think bad and negative thoughts concerning Allah, and is forbidden to have negative thoughts about a pious Muslim.

Negative assumptions are when you harbour a negative opinion about somebody which is believed to be something bad without any proof. There are two types of assumptions: 

1. The kind that enters the heart and then is openly expressed with the tongue, if this is something bad or evil towards another Muslim, it is then a sin.
2. Then the second kind is when it enters the heart but is not articulated on the tongue, although this is not a sin, you should still purify your heart from such negative thoughts.

The primary aim of those who suspect is their wish to establish the truth. However, in the Quran, truth is established through certainty. In contrast, suspicion is based on assumptions; assumptions is never a substitute for truth:

وَمَا لَهُم بِهِۦ مِنْ عِلْمٍۖ إِن يَتَّبِعُونَ إِلَّا ٱلظَّنَّۖ وَإِنَّ ٱلظَّنَّ لَا يُغْنِى مِنَ ٱلْحَقِّ شَيْـًٔا

And they have thereof no knowledge. They follow not except assumption, and indeed, assumption avails not against the truth at all.

(Qur'an: Surah An-Najm [the Star] 53, verse 28)

"Do not say, 

`I have seen', when you did not see anything, or 

`I have heard', when you did not hear anything, or 

`I know', when you do not know, 

for Allah will ask you about all of that."

The following Hadith is found in Sunan Abu Dawud:

بِيْسَ مَطِيَّةُ الرَّجُلِ زَعَمُوا

What an evil habit it is for a man to say, `They claimed...' 

According to another Hadith:

إِنَّ أَفْرَى الْفِرَى أَنْ يُرِيَ الرَّجُلُ عَيْنَيْهِ مَا لَمْ تَرَيَا

The worst of lies is for a man to claim to have seen something that he has not seen.

In the Sahih it says:

مَنْ تَحَلَّمَ حُلْمًا كُلِّفَ يَوْمَ الْقِيَامَةِ أَنْ يَعْقِدَ بَيْنَ شَعِيرَتَيْنِ وَلَيْسَ بِفَاعِل

Whoever claims to have seen a dream (when he has not seen) will be told on the Day of Resurrection to make a knot between two barley grains, and he will not be able to do it. 

كُلُّ أُولـيِكَ

each of those ones, means these faculties, hearing, sight and the heart,

كَانَ عَنْهُ مَسْوُولاً

will be questioned.

وَلَا تَقْفُ مَا لَيْسَ لَكَ بِهِۦ عِلْمٌۚ إِنَّ ٱلسَّمْعَ وَٱلْبَصَرَ وَٱلْفُؤَادَ كُلُّ أُو۟لَٰٓئِكَ كَانَ عَنْهُ مَسْـُٔولًا 

And do not pursue [do not assume & do not say] that of which you have no knowledge. Indeed, the hearing, the sight and the heart - about all those [one] will be questioned.

(Qur'an: Surah Al-Isra [the night journey] 17, verse 36)