It was narrated from Abu Hurayrah (radiAllahu anhu) that the Prophet (sallellahu alaihi wa sallam) said: “The first thing among their deeds for which the people will be brought to account on the Day of Resurrection will be PRAYER. Our Lord will say to His angels, although He knows best, ‘Look at My slave’s prayer, is it complete or lacking?’ If it is complete, it will be recorded as complete, but if it is lacking, He will say, ‘Look and see whether my slave did any voluntary (naafil) prayers.’ If he had done voluntary prayers, He will say, ‘Complete the obligatory prayers of My slave from his voluntary prayers.’ Then the rest of his deeds will be examined in a similar manner.”
[Narrated by Abu Dawood: 864].