Sahih al-Bukhari 1816

Abu al-Walid narrated to us; Shuba narrated to us, from Abd al-Rahman ibn al-Asbahani, from Abdullah ibn Maqil, who said: I sat with Kaab ibn Ujrah (may Allah be pleased with him) and asked him about the expiation. He said that it was revealed specifically concerning him, but applied generally to everyone. He was carried to the Messenger of Allah while lice were falling onto his face. The Prophet said that he had not thought the pain had reached this point, as he saw, or, according to another wording, that he had not thought the hardship had reached this point, as he saw. He asked whether Kaab could find a sheep. Kaab replied that he could not. The Prophet told him to fast for three days, or feed six needy people, giving each person half a saa.