What is the ruling on forgetting the final Tashahhud until the Imam says the Taslim, then performing it after the Taslim and the prostration of forgetfulness? And what is the correct action in this case?

Scholars differed as to whether what the latecomer (masbuq) apprehends with the Imam is the beginning of his prayer or its end. According to both opinions, he is not obligated to perform the prostration of forgetfulness (sujud sahv) if he misses the final tashahhud with the Imam. The correct view is that it is sunnah for the latecomer to follow the Imam in the final tashahhud, but this tashahhud is not obligatory for him nor is it considered valid for him. So, if he forgets it, the prostration of forgetfulness is not incumbent upon him. Repeating the final tashahhud after the salām is futile and not legislated. As for the prostration of forgetfulness, it was permissible before the salām.