What is the ruling regarding someone who sat after prostrating, then doubted whether it was the second or first prostration, so he completed the Tashahhud and prayers upon the Prophet (peace be upon him), then his doubt grew stronger so he made it the sitting between the two prostrations, then prostrated, then sat and recited the Tashahhud and made the Tasleem, and did not perform the prostration of forgetfulness (sujud al-sahw) due to persistent doubt?

The prayer of one who doubts having omitted a pillar while in the prayer is valid, and his ruling is the same as one who did not perform it. Thus, he must immediately perform it and complete his prayer, then prostrate for forgetfulness (sujud al-sahw) after the salutation (taslim). As for one who frequently doubts, he should not pay attention to it and should not prostrate for it. However, if he does pay attention to it and acts upon the minimum, his prayer is valid.