Narrated Abdullah bin Amr (Radi-Allahu 'anhu):
Allah's Apostle (Sallallahu 'Alaihi Wa Sallam) said to me, "The most
beloved fasting to Allah was the fasting of (the Prophet) David
('Alaihis-Salam) who used to fast on alternate days. And the most beloved
prayer to Allah was the prayer of David ('Alaihis-Salam) who used to sleep
for (the first) half of the night and pray for 1/3 of it and (again) sleep
for a sixth of it."
Bukhari Vol. 4 : No. 631