Sahih Bukhari

Narrated Ka`b bin Ujrah:The Prophet (ﷺ) came to me during the period of Al-Hudaibiya, while I was lighting fire underneath a cooking pot and lice were falling down my head. He said, ""Do your lice hurt your?"" I said, ""Yes."" He said, ""Shave your head and fast for three days or feed six poor persons or slaughter a sheep as a sacrifice: