What is the ruling on the prayer of one who imagined missing a rak'ah, so he stood up to perform it, then became certain that it was the fourth rak'ah, and performed the two prostrations of forgetfulness (sujud al-sahw) after the tashahhud and the Ibrahimiyyah prayer, then made the taslim?

If a worshiper doubts the number of rak'ahs (units of prayer), they should base it on the lesser, certain number, and perform the prostration of forgetfulness (sujood al-sahw). Re-performing the prayer is not obligatory, because the increase occurred due to forgetfulness. Al-Nawawi said: "If one doubts in their prayer whether they prayed three or four rak'ahs, for example, they must base it on certainty, so they must perform a fourth rak'ah and prostrate for forgetfulness, acting upon the hadith of Abu Sa'id, which is the saying of the Prophet, peace be upon him: 'If any of you doubts in his prayer and does not know how many he has prayed, three or four, let him cast away doubt and base it on what he is certain of, then let him prostrate twice before giving the salutations. If he has prayed five rak'ahs, they will intercede for his prayer, and if he has prayed a complete four, they will be a humiliation for Satan.'"