Sayyiduna Abu Huraira (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Those two men cannot be together in Paradise, one of whom said to his Muslim brother, 'O disbeliever.'"
Hadith Referenceمسند اسحاق بن راهويه / كتاب الجنة و النار و صفتهما / 977