Narrated Ka`b bin Ujra:That Allah's Messenger (ﷺ) saw him with the lice falling (from his head) on his face. Allah's Messenger (ﷺ) said, "Are your lice troubling you? Ka`b said, "Yes." Allah's Messenger (ﷺ) thus ordered him to shave his head while he was at Al-Hudaibiya. Up to then there was no indication that all of them would finish their state of Ihram and they hoped that they would enter Mecca. Then the order of Al-Fidya was revealed, so Allah's Messenger (ﷺ) ordered Ka`b to feed six poor persons with one Faraq of food or slaughter a sheep or fast for three days

English translation · Sahih al-Bukhari