Abu Malikah narrated that a man came to Abu Bakr Siddiq (may Allah be pleased with him), and another man had bitten him with his teeth, so he pulled his hand away from him and one of his front teeth fell out. Abu Bakr (may Allah be pleased with him) said, "His front tooth is lost in vain."
Hadith Referenceمسند الإمام الشافعي / كتاب العتق / 1670
Hadith Takhrijاخرجه البخاري، الإجارة، باب الأجير في الغزو (2266)۔