Abd al-Rahman bin Abi Layla (may Allah have mercy on him) narrates from Ka'b bin Ujrah (may Allah be pleased with him) that this verse was revealed about me: I came to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Come closer." I came closer two or three times, and he (peace and blessings be upon him) asked: "Are your lice troubling you?" I think he said: "Yes."
(b) Ayyub reports these words from Mujahid: "Have the lice of your head troubled you?" Then he (peace and blessings be upon him) ordered me to fast, give charity or offer a sacrifice, whichever was easy. Ibn Awn said: Mujahid had explained it to me, but I forgot. Ayyub informed me that he heard from Mujahid: fasting three days, or charity to six poor people, or the sacrifice of a goat.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9793