Mishkat al-Masabih

Ka‘b b. ‘Ujra told that the Prophet (ﷺ) came upon him at al-Hudaibiya while he was still in the sacred state before entering Mecca. He was kindling a fire under a pot and lice were falling in large numbers over his face. He asked him whether the insects were annoying him, and when he replied that they were, he said, “Shave your head, and give a faraq (i.e. three sa‘s) to six poor people, or fast three days, or sacrifice an animal.” Bukhari and Muslim.