Prayer at Night (Tahajjud)

Bukhari :: Book 2 :: Volume 21 :: Hadith 236

Narrated Abu-Wa il:

'Abdullah said, "One night I offered the Tahajjud prayer with the Prophet and he kept on standing till an ill-thought came to me." We said, "What was the ill-thought?" He said, "It was to sit down and leave the Prophet (standing)."