Sunan an-Nasa'i

It was narrated that Ghudaif bin Al-Harith said: "I entered upon 'Aishah and asked her: “Did the Messenger of Allah (ﷺ) perform Ghusl at the beginning of the night or at the end?' She said: “Both. Sometimes he performed Ghusl at the beginning and sometimes at the end.' I said: “Praise be to Allah who has made the matter flexible”””"