That he was with the Messenger of Allah in Ihram and he suffered an infestation of head lice. The Messenger of Allah commanded him to shave his head and told him: "Fast for three days, or fed six poor persons two Mudds earch, or sacrifice a sheep. Whichever one of these you do will be sufficient for you.'" (Using translation from Nasāʾī 2851)  

أَنَّهُ كَانَ مَعَ رَسُولِ اللهِ ﷺ مُحْرِمًا فَآذَاهُ الْقَمْلُ فَأَمَرَهُ رَسُولُ اللهِ ﷺ أَنْ يَحْلِقَ رَأْسَهُ وَقَالَ «صُمْ ثَلَاثَةَ أَيَّامٍ أَوْ أَطْعِمْ سِتَّةَ مَسَاكِينَ مُدَّيْنِ مُدَّيْنِ أَوِ انْسُكْ شَاةً أَيَّ ذَلِكَ فَعَلْتَ أَجْزَأَ عَنْكَ»  

"I entered Ihram, then I had a severe infestation of head lice. News of that reached Prophet, and he came to me when I was cooking something in a pot for my companions, he touched my head with his finger and said: 'Go and shave it, and give charity to six poor persions.'". (Using translation from Nasāʾī 2852)  

أَحْرَمْتُ فَكَثُرَ قَمْلُ رَأْسِي فَبَلَغَ ذَلِكَ النَّبِيَّ ﷺ فَأَتَانِي وَأَنَا أَطْبُخُ قِدْرًا لِأَصْحَابِي فَمَسَّ رَأْسِي بِإِصْبَعِهِ فَقَالَ «انْطَلِقْ فَاحْلِقْهُ وَتَصَدَّقْ عَلَى سِتَّةِ مَسَاكِينَ»