Musnad Abu Ya'la al-Mawsili 140:39

Abu al-Rabi' al-Zahrani narrated to us, Hammad narrated to us, Yazid al-Raqashi narrated to us, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the first thing Allah made obligatory upon the people from their religion is the prayer, and the last thing that will remain is the prayer, and the first thing they will be held accountable for is the prayer. Allah will say: 'Look into the prayer of My servant; if it is complete, it is recorded as complete, and if it is found to be deficient, He will say: Look, does he have any voluntary [prayers]? If voluntary [prayers] are found for him, the obligatory [prayer] is completed from the voluntary [prayers].' Then He will say: 'Look, is his Zakat complete? If his Zakat is found to be complete, it is recorded as complete, and if it is deficient, He will say: Look, does he have any charity? If he has charity, his Zakat is completed for him from the charity.'"