The ruling on one who sits for the first tashahhud after the third rak'ah in making up a missed prayer

Question:
A man prayed with the imam and caught the last rak'ah of the 'Asr prayer. After the imam finished the prayer, he stood up to complete the prayer, but he sat for the first tashahhud after the third rak'ah. What is the ruling on his prayer?

Answer:
The prayer is valid, but the tashahhud he delayed from its proper place is obligatory to be performed after the second rak'ah, following the taslim. If he stands up and reaches the second rak'ah after the taslim, he sits, then stands up and performs the rak'ah in it; this is the place for the tashahhud. So he moved it from its place and placed it after three rak'ahs, which is not its place. This means he left out the first tashahhud. If he remembers, whether he is in the prayer or after the prayer, and the delay is short, he prostrates two prostrations for forgetfulness. If the interval is long, his prayer is valid, or the prostration for forgetfulness is dropped from him due to forgetfulness.