Musnad Abu Ya'la al-Mawsili 115:101

Abu Yusuf al-Jizi narrated to us, Abdullah bin al-Walid al-Adani narrated to us, from Sufyan, from Ma’mar, from Qatadah, from Anas, that the Prophet (peace and blessings of Allah be upon him) used to go around to his wives with a single ritual bath (ghusl). This means that he went around to his wives in one night and performed a single ritual bath.