Musannaf Ibn Abi Shayba 1:869

Abu Bakr narrated to us, he said: Hafs narrated to us, from 'Asim, from Abu al-Mutawakkil, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If one of you has intercourse with his wife at night, then wishes to repeat it, let him perform ablution between them—an ablution."