Sayyiduna Samurah (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) forbade us from reviling, and he said: "If one of you must inevitably revile his companion, then let him not make a false accusation against him, nor revile his parents, nor revile his people. Rather, if he knows (some fault in him), let him say: 'You are stingy,' or let him say: 'You are a coward,' or let him say: 'You are a liar,' or let him say: 'You are base.'"
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 7000