THE DANGER OF TAUNTING SOMEONE REGARDING A SIN
Huzoor e Aqdas (Rasulullah)ﷺ said: That person who taunts and ridicules his Muslim brother over a sin from which he has repented, will not die until he himself commits that same sin. E.g. you come to know that a certain person committed or was involved in a particular sin. You also know that he has made Taubah (repented) from it. To think low of him or to taunt and ridicule him because of that sin by saying that, “you are the one who was involved in certain evil actions,” is in itself a sin.
Through repentance a person has corrected his relationship with Allah Ta’aala. Through repentance not only has the sin been forgiven, it has also been erased from his book of deeds! Allah Ta’aala has erased it from his book of deeds but you, because of that sin, are thinking low of him and treating him with contempt. You are taunting and ridiculing him. This action is extremely despised by Allah Ta’aala.