What is the ruling on one who completes their prayer without remembering what they said in it, and is that considered forgetting a pillar or a duty, and what are the consequences of that?

If someone doubts having omitted a pillar (rukn) or an obligation (wajib) after completing the prayer, they should disregard their doubt, because doubt after completing an act of worship has no effect. However, if someone doubts during the prayer: if they are prone to frequent doubts, they should ignore the doubt, and prostration of forgetfulness (sujud al-sahw) is not prescribed for them. But if they are not prone to frequent doubts, and they doubt having omitted a pillar, they should perform it and what comes after it, dismiss the doubt, and build upon what they are certain of. As for someone who performed the pillars and obligations of the prayer but whose heart was heedless, they have erred by abandoning devotion (khushu'), but their prayer is valid and fulfills the obligation, and they are not required to repeat it. Some scholars, however, held that devotion is obligatory, contrary to the majority.