It is narrated from Hazrat Ka'b (may Allah be pleased with him) that once he was with the Holy Prophet (peace and blessings be upon him) and the lice on his head were causing him great distress. The Holy Prophet (peace and blessings be upon him) ordered him to shave his head and said: "Fast for three days, or feed six needy people, each with two mudd of food, or offer a sacrifice of one goat. Whatever you do will suffice for you."