Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) said that when they were at al-Hudaybiyah, before entering Makkah, the Messenger of Allah (peace and blessings be upon him) passed by him while he was lighting a fire under his cooking pot, and lice were falling onto his face. He (peace and blessings be upon him) said: "Are these lice of yours troubling you?" I said: "Yes!" He (peace and blessings be upon him) said: "Then shave your head and feed one faraq to six poor people" - and a faraq is three sa' - "or fast three days, or offer a sacrifice."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9093