Must prayers that were performed with traces of urine on the underwear be repeated, when it was discovered after the prayer, knowing that it was present before it?

If someone prays while there is impurity on their garment and they do not become aware of it until after finishing the prayer, then they are not required to repeat the prayer, and their prayer is valid. The evidence for this is that the Prophet, peace and blessings be upon him, once prayed while there was dirt on his sandals, so he removed them during the prayer and did not restart the prayer.