Sahih Bukhari | Volume 7 | Hadith Number 604
Narrated by Ka'b bin Ujrah
The Prophet 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."