Musnad Ahmad 30:111

'Abd al-Rahman narrated to us, from Malik, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Beware of continuous fasting (wisal), beware of continuous fasting, beware of continuous fasting" — that is how my knowledge is. They said: "You yourself 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."