Musnad Ahmad 789:14

Aswad ibn Amir Shadhan narrated to us, Abu Bakr—meaning Ibn Ayyash—narrated to us, from al-A’mash, from Sa’id ibn ‘Abdullah ibn Jurayj, from Abu Barzah al-Aslami, who said: The Messenger of Allah (ﷺ) said: "O assembly of those who have believed with their tongues while faith has not entered their hearts, do not backbite the Muslims, and do not pursue their faults. For whoever pursues their faults, Allah will pursue his fault, and whoever Allah pursues his fault, He will expose him [even if he is] in his house."