“O you who Believe avoid much suspicion, indeed some suspicion is a sin. And spy not on one an other neither backbite one another.”
[49:12]

It is collected in Bukhari and Muslim and narrated upon the authority of Abu Hurairah that the Messenger Muhammad (saw) said:

“Beware of suspicion, for suspicion is the worst of false tales. Do not look for others faults, do not spy on one another, do not practice najash (biding over one another), do not be jealous of one another, do not hate one another and do not desert or stop talking to one another. O Allah’s worshippers, be brothers”.

It is reported by Muslim upon the authority of Abu Hurairah and in Ahmad upon the authority of Abu Barza Al-Aslami (ra) that the Messenger Muhammad (saw) said:

“O you who believe from your tongues but whose Imaan has never settled in their hearts. Do not backbite Muslims, do not follow up their aworaat (e.g. spying on them or tracing their errors and personal affairs); whoever does so Allah will punish him for all his errors and will expose his affairs even if he is settled in his own home”