Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Hisham bin ‘Amir (may Allah be pleased with him), he states that I heard the Messenger of Allah (peace and blessings be upon him) say: “It is not permissible for any Muslim to sever relations with his brother for more than three days. As long as they persist in this forbidden act, they will remain deviated from the right path. Whoever takes the lead in reconciliation, his initiative will be an expiation for his sin. If he greets (with salam) but the other does not reply, then the angels will respond to him and Satan will descend upon the other. If they die in this state of severed relations, they will never enter Paradise.”