Musannaf Ibn Abi Shayba 3:5394

Hushaym narrated to us, from Dawud ibn Abi Hind, from Zurarah ibn Awfa, from Tamim al-Dari, who said: "Indeed, the first thing the servant will be held accountable for is the prayer. If he completed it, [it is accepted]. Otherwise, it will be said: 'Look, does he have any voluntary [prayers]?' If he has any voluntary [prayers], then complete the obligatory [prayers] from the voluntary ones."