(35) باب غَزْوَةِ الْحُدَيْبِيَةِ
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.
Reference: Sahih al-Bukhari 4159
In-book reference: Book 64, Hadith 202
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 59, Hadith 478