Qur'an, Al-Hujurat, Surah 49:12-13
Believers, keep away from excessive suspicion, for suspicion in some cases is a grave crime. Do not spy, nor backbite one another. Would any one of you like to eat the flesh of a dead brother? You certainly abhor that so abhor the other! Remain conscious of Allah, for Allah verily is the Most Relenting and Merciful.