Sayyiduna Ka'b bin 'Ujrah (may Allah be pleased with him) says that during Hudaybiyyah, the Messenger of Allah (peace and blessings be upon him) was standing by me and lice were falling from my head. The Prophet (peace and blessings be upon him) said: "Are the lice troubling you?" I replied, "Yes." So the Prophet (peace and blessings be upon him) said: "Shave your head." (Ka'b, may Allah be pleased with him, says:) It was concerning me that this verse was revealed: "And whoever among you is ill or has an ailment of the head (necessitating shaving), then..." (__QUR_N__ al-Baqarah: 196). So the Noble Prophet (peace and blessings be upon him) said: "Fast three days, or feed six needy people, or offer whatever sacrifice is available."