Musnad Ahmad 28:443

Muhammad ibn Bakr and Abd al-Razzaq narrated to us, they said: Ibn Jurayj narrated to us. And Rawh said: Ibn Jurayj informed us, Amr ibn Dinar informed me, that Amr ibn Aws informed him, from Abdullah ibn Amr ibn al-Aas, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The most beloved fasting to Allah is the fasting of David; he used to fast half of the lifetime. And the most beloved prayer to Allah is the prayer of David; he used to sleep half of the night, then stand [in prayer], then sleep the last part of it, then stand [in prayer] for a third of the night after its half."