What is the ruling on the Fajr prayer for someone who remembered, while in the last Tashahhud, that they had not bowed, so they completed an entire rak‘ah, believing that it is prescribed for whoever remembers a pillar before or after the taslim to perform a complete rak‘ah?

If someone forgets the bowing (rukūʿ) in the last rakʿah and remembers it before the taslīm (salutation), they must stand up and perform the bowing, then sequentially perform the actions that follow the bowing in the prayer. This is because the actions performed after the missed pillar are not considered valid due to the disruption of the sequence. It is not obligatory for them to repeat the recitation before the bowing.

Scholars differed on whether one should stand up then bow, or stand up already in the bowing position. The well-known opinion is that one should stand up then bow.

If someone repeats the recitation of Surat al-Fatihah and another surah out of ignorance or in adherence to the opinion of some jurists, their prayer is valid. An unprescribed addition does not invalidate the prayer unless it is done intentionally. However, if it is done out of forgetfulness or ignorance, it does not invalidate the prayer.