Prayer at Night (Tahajjud)
Bukhari :: Book 2 :: Volume 21 :: Hadith 230
The Prophet used to stand (in the prayer) or pray till both his feet or legs swelled. He was asked why (he offered such an unbearable prayer) and he said, "should I not be a thankful slave."
Source materials are from the University of Southern California MSA site|
Hadith eBooks converted from Imaan Star