A worshiper who remembers that he missed an obligatory step of ablution after he had finished praying will have to repeat
Answer Details
If a worshipper remembers after completing his prayer that he missed an obligatory step of ablution, he will have to repeat both the ablution and the prayer. This is because the prayer is not considered valid without the proper performance of ablution, and missing an obligatory step in the ablution breaks the continuity of the required ritual purity. Therefore, the worshipper must redo the ablution and the prayer to ensure that the act of worship is valid in the eyes of God.