It is narrated from Sayyiduna Imran bin Husayn (may Allah be pleased with him) that a man bit another man's hand, so he pulled his hand out of his mouth and his front tooth came out, "and the Prophet (peace and blessings be upon him) declared it unavenged (with no compensation)" - or he said: "and the Prophet (peace and blessings be upon him) declared it void."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15624