What is the ruling on the prayer of an individual who, after rising from rukūʿ, did not stand for a sufficient duration to say "Samiʿa Allāhu liman ḥamidah" (Allah hears those who praise Him) or "Subḥānallāh" (Glory be to Allah), and is prostration of forgetfulness (sujūd as-sahw) required in this case?

If a solitary worshiper says "Rabbana wa lakal-hamd" (Our Lord, and to You be all praise) while descending [for prostration], his prayer is valid. And moderation (al-i'tidal) after rising from bowing is a pillar, and it is achieved when the worshiper stands upright and his limbs become still, even if for a brief moment, even if he does not remain for the duration of a specific remembrance. If he does not perform the sufficient amount of moderation, his prayer becomes invalid, and this pillar is not forfeited intentionally or by oversight.