كتاب الحيض
3  
The Book of Menstruation
(3)
Chapter: It is permissible for a menstruating woman to wash her husband’s head, and comb his hair; her leftovers are pure (tahir); and regarding reclining in her lap and reciting Qur’an
(3)
باب جَوَازِ غَسلِ الْحَائِضِ رَأْسَ زَوْجِهَا وَتَرْجِيلِهِ وَطَهَارَةِ سُؤْرِهَا وَالاِتِّكَاءِ فِي حِجْرِهَا وَقِرَاءَةِ الْقُرْآنِ فِيهِ
Sahih Muslim 297 a

It is reported from 'A'isha that she observed:

When the Messenger of Allah (ﷺ) was in I'tikaf, he inclined his head towards me and I combedhis hair, and he did not enter the house but for the natural calls (for relieving himself).
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنِ ابْنِ شِهَابٍ، عَنْ عُرْوَةَ، عَنْ عَمْرَةَ، عَنْ عَائِشَةَ، قَالَتْ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا اعْتَكَفَ يُدْنِي إِلَىَّ رَأْسَهُ فَأُرَجِّلُهُ وَكَانَ لاَ يَدْخُلُ الْبَيْتَ إِلاَّ لِحَاجَةِ الإِنْسَانِ ‏.‏
Reference : Sahih Muslim 297a
In-book reference : Book 3, Hadith 6
USC-MSA web (English) reference : Book 3, Hadith 582
  (deprecated numbering scheme)