Musnad Ahmad 31:69

Qutaybah narrated to us, Bakr ibn Mudar narrated to us, from Ibn al-Had, from Abdullah ibn Khabbab, from Abu Sa’id al-Khudri, that he heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Do not practice continuous fasting (wisal). Whoever among you wishes to practice continuous fasting, let him continue until the suhoor (pre-dawn meal)." They said: "But you practice continuous fasting." He said: "I am not like you. I spend the night with One who feeds me and gives me to drink."