Sahih Bukhari Volume 003, Book 031, Hadith Number 187.

Narated By Abu Huraira : The Prophet said twice, "(O you people) Be cautious! Do not practice Al-Wisal." The people said to him, "But you practice Al-Wisal?" The Prophet replied, "My Lord gives me food and drink during my sleep. Do that much of deeds which is within your ability."