Sahih Muslim 297
Sahih Muslim · Book 3: The Book of Menstruation · 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
Al-Aswad narrated it from 'A'isha that she observed:
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا حُسَيْنُ بْنُ عَلِيٍّ ، عَنْ زَائِدَةَ ، عَنْ مَنْصُورٍ ، عَنْ إِبْرَاهِيمَ ، عَنِ الأَسْوَدِ ، عَنْ عَائِشَةَ ، قَالَتْ كُنْتُ أَغْسِلُ رَأْسَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَنَا حَائِضٌ .
I used to wash the head of the Messenger of Allah (ﷺ), while I was in a state of menstruation.