What is the ruling on the prayer of one who led the congregational prayer due to the imam's absence, despite there being someone more deserving than him, then added an extra bowing (ruku') in the second rak'ah, performed only one prostration of forgetfulness (sajdat al-sahw) before the taslim, and his takbir was not heard when rising from it, and he made the taslim while the congregants were still prostrating?

If the Imam adds an extra bowing (ruku'), he must return to the standing position and then prostrate. He should then perform the prostration of forgetfulness (sujud (definition) al-sahw) after the salām. If he prostrates directly from the bowing, the Shāfiʿīs hold that his prayer is invalid because descending to prostration must be with the intention of prostrating, not with the intention of bowing. As for the Mālikīs, their relied-upon position is that the intention for the transition is not obligatory. Therefore, the Imam's prostration directly from the bowing does not invalidate the prayer, but he is prescribed to perform the prostration of forgetfulness before the salām. Given the situation described, there is no harm in adopting the view of the Mālikīs and ruling the prayer valid, knowing that the prostration of forgetfulness consists of two prostrations and is a sunnah (definition), the omission of which does not invalidate the prayer according to the majority of scholars.