Musnad Ahmad 541:11

Yazid narrated to us, Musa narrated to us, he said: I heard my father saying: Abu Qays, the freed slave of ‘Amr ibn al-‘As, narrated to me that ‘Amr ibn al-‘As used to fast continuously, and he rarely ate dinner at the beginning of the night; most of what he would eat was at the time of the suhur (pre-dawn meal). He said: And I heard him saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Indeed, the distinction between our fasting and the fasting of the People of the Book is the meal of the suhur."