What is the ruling on one who prostrated for forgetfulness (sujud al-sahw) after the tasleem, out of ignorance of the ruling on what he had done in the prayer?

Reciting the supplication for riding unintentionally during prayer does not necessitate prostration of forgetfulness (sujud al-sahw), as it is a prescribed remembrance. Similarly, repeating the tashahhud unintentionally also does not entail sujud al-sahw, because it is an additive verbal act from what is prescribed in prayer. If a worshipper makes an unintentional error in Al-Fatiha that changes its meaning, and then corrects it, then sujud al-sahw is prescribed in this case, because it is considered obligatory by some jurists. If sujud al-sahw is performed out of ignorance without a reason, the prayer is not invalidated.