Riyad us Saliheen: Hadith 1176

The Messenger of Allah (ﷺ) said, "The Salat which is dearest to Allah is that of (Prophet) Dawud; and As-Saum (the fasting) which is dearest to Allah is that of (Prophet) Dawud. He used to sleep half the night, get up to perform Salat for one-third of it, then sleep through the remaining one-sixth of it; and he used to observe Saum on alternative days."

[Al-Bukhari and Muslim].