What did the Prophet Muhammad (peace be upon him) advise Ka'b b. 'Ujra (Allah be pleased with him) to do, when he (saw) noticed the lice on Ka'b's face?
 Ka'b b. 'Ujra (Allah be pleased with him) reported:                      The Messenger of Allah (may peace be upon him) came to me on the occasion of Hudaibiya and I was kindling fire under my cooking pot and lice were creeping on my face. Thereupon he (the Holy Prophet) said: Do the vermins harm your head? I said: Yes. He said: Get your head shaved and (in lieu of it) observe fasts for three days or feed six needy persons, or offer sacrifice (of an animal). Ayyub said: I do not know with what (type of expiation) did he commence (the statement).