What advice did Prophet Muhammad (saw) give to Ka'b bin Ujrah when he noticed lice were falling down from his head?
 Narrated 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:"