What is the ruling on one who doubts whether they have performed a prescribed prayer or not?

Whoever doubts whether he has prayed an obligatory prayer or not, he should dismiss the doubt and pray, because prayer is a debt upon one's conscience that can only be discharged with certainty. If one who doubts the number of rak'ahs builds upon the lesser number, then what about one who doubts the prayer itself? Al-Baghawi said: "Whoever doubts whether he has prayed or not, he is obligated to repeat it." As for the one afflicted with waswasah (obsessive whispering), he should not pay attention to the doubt if he predominantly believes he has prayed.