كتاب الحيض
3  
The Book of Menstruation
(10)
Chapter: 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
(10)
باب الْقَدْرِ الْمُسْتَحَبِّ مِنَ الْمَاءِ فِي غُسْلِ الْجَنَابَةِ وَغُسْلِ الرَّجُلِ وَالْمَرْأَةِ فِي إِنَاءٍ وَاحِدٍ فِي حَالَةٍ وَاحِدَةٍ وَغُسْلِ أَحَدِهِمَا بِفَضْلِ الآخَرِ
Sahih Muslim 321 c

'A'isha reported:

I and the Messenger (ﷺ) took a bath from the same vessel and our hands alternated into it in the state that we had had sexual intercourse.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، قَالَ حَدَّثَنَا أَفْلَحُ بْنُ حُمَيْدٍ، عَنِ الْقَاسِمِ بْنِ مُحَمَّدٍ، عَنْ عَائِشَةَ، قَالَتْ كُنْتُ أَغْتَسِلُ أَنَا وَرَسُولُ اللَّهِ، صلى الله عليه وسلم مِنْ إِنَاءٍ وَاحِدٍ تَخْتَلِفُ أَيْدِينَا فِيهِ مِنَ الْجَنَابَةِ ‏.‏
Reference : Sahih Muslim 321c
In-book reference : Book 3, Hadith 53
USC-MSA web (English) reference : Book 3, Hadith 629
  (deprecated numbering scheme)