a man bit another man in the forearm, and his front tooth fell out, so he went to the Prophet and told him about that. He said: "Do you want to bite your brother's forearm as a stallion bites?" And he judged it to be invalid.
Reference: Sunan an-Nasa'i 4762 In-book : Book 45, Hadith 57 English translation : Vol. 5, Book 45, Hadith 4766
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