All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is Islamically established that in principle a Muslim is innocent, so it is not permissible for someone to accuse him of something abominable without evidence; Allaah Says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin.}[Quran 49:12]
Based on the innocence of the accused, he is the one who should be believed unless the contrary is proven; for more benefit, please refer to Fatwa 138768.
Finally, it should be noted that a Muslim should fear Allaah in regard to the honor of his fellow Muslim; Abu Hurayrah narrated that the Prophet said: “All things of a Muslim are inviolable for another Muslim: his blood, his wealth and his honor.”
Allaah Knows best.