Sahih Muslim
Sahih Muslim 1201 b
It is permissible for a Muhrim to shave his head if there is a problem, but it is obligatory to offer a Fidyah for shaving it, and Clarifying what the Fidyah is
Arabic hadith text
حَدَّثَنِي عَلِيُّ بْنُ حُجْرٍ السَّعْدِيُّ، وَزُهَيْرُ بْنُ حَرْبٍ، وَيَعْقُوبُ بْنُ إِبْرَاهِيمَ، جَمِيعًا عَنِ ابْنِ عُلَيَّةَ، عَنْ أَيُّوبَ، فِي هَذَا الإِسْنَادِ . بِمِثْلِهِ
Translation
This hadith is narrated on the authority of Ayyub.