(1) The Book of Purification and its Sunnah
كتاب الطهارة وسننها
(101) Chapter: One who has one bath after being intimate with all his wives
(101) باب مَا جَاءَ فِيمَنْ يَغْتَسِلُ مِنْ جَمِيعِ نِسَائِهِ غُسْلاً وَاحِدًا
Sunan Ibn Majah 589 
It was narrated that Anas said:
"I put out water for the Messenger of Allah for a bath, and he had a bath after going to all of his wives in one night."
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، عَنْ صَالِحِ بْنِ أَبِي الأَخْضَرِ، عَنِ الزُّهْرِيِّ، عَنْ أَنَسٍ، قَالَ وَضَعْتُ لِرَسُولِ اللَّهِ ـ صلى الله عليه وسلم ـ غُسْلاً فَاغْتَسَلَ مِنْ جَمِيعِ نِسَائِهِ فِي لَيْلَةٍ ‏.‏
Grade :  Da'if (Darussalam)
Reference : Sunan Ibn Majah 589
In-book reference : Book 1, Hadith 323
English translation : Vol. 1, Book 1, Hadith 589