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 c

'A'isha, the wife of the Apostle (may peace he upon him), reported:

The Messenger of Allah (ﷺ) put out from the mosque his head for me as he was in I'tikaf, and I washed it in the state that I was menstruating.
وَحَدَّثَنِي هَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، حَدَّثَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي عَمْرُو بْنُ الْحَارِثِ، عَنْ مُحَمَّدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ نَوْفَلٍ، عَنْ عُرْوَةَ بْنِ الزُّبَيْرِ، عَنْ عَائِشَةَ، زَوْجِ النَّبِيِّ صلى الله عليه وسلم أَنَّهَا قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُخْرِجُ إِلَىَّ رَأْسَهُ مِنَ الْمَسْجِدِ وَهُوَ مُجَاوِرٌ فَأَغْسِلُهُ وَأَنَا حَائِضٌ ‏.‏
Reference : Sahih Muslim 297c
In-book reference : Book 3, Hadith 8
USC-MSA web (English) reference : Book 3, Hadith 584
  (deprecated numbering scheme)