Sahih Bukhari

Narrated `Abdur-Rahman bin Abu Layla:Ka`b bin 'Ujra said that Allah's Messenger (ﷺ) said to him (Ka`b), ""Perhaps your lice have troubled you?"" Ka`b replied, ""Yes! O Allah's Messenger (ﷺ)."" Allah's Messenger (ﷺ) said, ""Have your head shaved and then either fast three days or feed six poor persons or slaughter one sheep as a sacrifice