(3) The Book of Menstruation and Istihadah
كتاب الحيض والاستحاضة
(21) Chapter: A Menstruating Woman Washing Her Husband's Head
(21) باب غَسْلِ الْحَائِضِ رَأْسَ زَوْجِهَا
Sunan an-Nasa'i 387 
It was narrated that 'Aishah said:
"The Prophet (ﷺ) would put his head out while he was performing I'tikaf and I would wash it, while I was menstruating."
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنِي سُفْيَانُ، قَالَ حَدَّثَنِي مَنْصُورٌ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُدْنِي إِلَىَّ رَأْسَهُ وَهُوَ مُعْتَكِفٌ فَأَغْسِلُهُ وَأَنَا حَائِضٌ ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 387
In-book reference : Book 3, Hadith 40
English translation : Vol. 1, Book 3, Hadith 387