Musannaf Ibn Abi Shayba 1:679

Abu Bakr ibn Abi Shaybah narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Burayd ibn Sinan, from ‘Ubadah ibn Nusayy, from Ghudayf ibn al-Harith, who said: I came to ‘Aishah and said: "Have you seen the Messenger of Allah, may Allah bless him and grant him peace, in the beginning of the night, did he perform ghusl (full ablution) for janabah (major ritual impurity), or in its latter part?" She said: "Sometimes he would perform ghusl in the beginning of the night, and sometimes he would perform ghusl in its latter part."