What is the ruling regarding the 'Isha and 'Asr prayers if one discovers the presence of impurities in the underwear at the anal area after returning from the 'Isha prayer, and it is probable that they have been present since the 'Asr prayer?

The jurists differed regarding someone who prayed while there was an impurity on his garment, of which he was unaware, then became aware of it after the prayer. There are three views: His prayer is not invalidated—and this is the most preponderant view and the madhhab (definition) of many Companions and Tabi'un—or he must repeat the prayer, or he must repeat it if there is still time.