Sahih Muslim 321
Sahih Muslim · Book 3: The Book of Menstruation · The amount of water with which it is recommended to perform ghusl in the case of janabah; a man and woman washing from a single vessel; one of them washing with the left-over water of the other
'A'isha reported:
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى ، أَخْبَرَنَا أَبُو خَيْثَمَةَ ، عَنْ عَاصِمٍ الأَحْوَلِ ، عَنْ مُعَاذَةَ ، عَنْ عَائِشَةَ ، قَالَتْ كُنْتُ أَغْتَسِلُ أَنَا وَرَسُولُ اللَّهِ، صلى الله عليه وسلم مِنْ إِنَاءٍ - بَيْنِي وَبَيْنَهُ - وَاحِدٍ فَيُبَادِرُنِي حَتَّى أَقُولَ دَعْ لِي دَعْ لِي . قَالَتْ وَهُمَا جُنُبَانِ .
I and the Messenger of Allah (ﷺ) took a bath from one vessel which was placed between me and him and he would get ahead of me, so that I would say: Spare (some water for) me, spare (some water for) me; and she said that they had had sexual intercourse.