Abu Shurayh (a Companion) narrated that the Prophet of Allah, sallallaahu ‘alayhi wa sallam, said: “By Allah he is not a [true] believer, by Allah he is not a [true] believer, by Allah he is not a [true] believer.” People asked: “Who is that, O Messenger of Allah.” He, sallallaahu ‘alayhi wa sallam, replied: “The one whose neighbor is not safe from his evil.”
Ibn Hajar said: “This narration is a clear sign of the right of the neighbor, for the Prophet of Allah, sallallaahu ‘alayhi wa sallam, swore on this matter three times. It also negates faith from a person who harms his neighbor by his speech, or actions; meaning that he does not have perfect faith, for it is known that a sinner has not completed faith [..] the narration negates the perfection of faith from the one who harms his neighbor as a way of reflecting the great right of the neighbor and it proves that harming him is one of the grave major sins.