Sahih al-Bukhari 4517
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
The Statement of Allah "And whosoever of you is ill or has an ailment in his scalp..." (V.2:196)
Narrated `Abdullah bin Maqal: I sat with Ka`b bin Ujra in this mosque, i.e. Kufa Mosque, and asked him about the meaning of: "Pay a ransom (i.e. Fidya) of either fasting or . . . . (2:196)" He said, "I was taken to the Prophet (ﷺ) while lice were falling on my face. The Prophet (ﷺ) said, 'I did not think that your trouble reached to such an extent. Can you afford to slaughter a sheep (as a ransom for shaving your head)?' I said, 'No.' He said, 'Then fast for three days, or feed six poor persons by giving half a Sa of food for each and shave your head.' So the above Verse was revealed especially for me and generally for all of you."