Musannaf Ibn Abi Shayba 27:251

'Affan narrated to us, he said: Ja'far ibn Sulayman narrated to us, from Thabit al-Bunani, he said: It reached us that Dawud (David), the Prophet of Allah, divided the prayer among his households, his wives, and his children. There would not come an hour of the night or the day except that a person from the family of Dawud was standing and praying. So this verse encompassed them: "Work, O family of Dawud, in gratitude. And few of My servants are grateful."