Narrated ‘Abdur-Rahman bin Abu Layla:
Ka’b bin ‘Ujra said that Allah’s Apostle said to him (Ka’b), “Perhaps your lice have troubled you?” Ka’b replied, “Yes! O Allah’s Apostle.” Allah’s Apostle said, “Have your head shaved and then either fast three days or feed six poor persons or slaughter one sheep as a sacrifice.”
Sahih Bukhari, Volume 3, Book28, Number 41