Musnad Ahmad 1018:23

Waki’ narrated to us, Sufyan narrated to us, from ‘Abd al-Rahman ibn ‘Abis, from ‘Abd al-Rahman ibn Abi Layla, from some of the companions of Muhammad, may Allah bless him and grant him peace, who said: The Messenger of Allah, may Allah bless him and grant him peace, only forbade cupping for the fasting person and continuous fasting (wisal) out of consideration for his companions; he did not declare them unlawful. They said: "O Messenger of Allah, but you practice continuous fasting." He said: "I am not like one of you; I spend the night while my Lord feeds me and gives me drink."