Sahih al-Bukhari 3420

قَالَ لِي رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ أَحَبُّ الصِّيَامِ إِلَى اللَّهِ صِيَامُ دَاوُدَ، كَانَ يَصُومُ يَوْمًا وَيُفْطِرُ يَوْمًا، وَأَحَبُّ الصَّلاَةِ إِلَى اللَّهِ صَلاَةُ دَاوُدَ، كَانَ يَنَامُ نِصْفَ اللَّيْلِ وَيَقُومُ ثُلُثَهُ وَيَنَامُ سُدُسَهُ ‏"‏‏.

“Allah's Messenger ﷺ said to me, "The most beloved fasting to Allah was the fasting of (the Prophet) David who used to fast on alternate days. And the most beloved prayer to Allah was the prayer of David 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”