If a servant is obligated to re-perform a fard (obligatory) prayer, and discovers this after having performed many subsequent prayers, does he re-perform that prayer and all those that followed it, or does he re-perform only that prayer, and does he re-perform it along with its counterparts or at any time?

Whoever's prayer becomes invalid must repeat it at any time of day or night, without waiting for the time of its equivalent prayer. He is not obligated to repeat the valid prayers he performed after the invalid prayer, for an obligatory prayer is legislated to be performed only once, unless there is a reason necessitating its repetition.