Abu Dharr (May Allah be pleased with him) said:
I heard the Messenger of Allah (ﷺ) saying, "If somebody accuses another of disbelief or calls him the enemy of Allah, such an accusation will revert to him (the accuser) if the accused is innocent."[Al-Bukhari and Muslim].
App reference: Book 18, Hadith 223
Arabic/English book reference: Book 18, Hadith 1733