The ruling on one who doubts about impurity after the taslim

The Shaykh : It is not known to be upon him. For two reasons; we explain that with two reasons. The first reason is that his prayer has ended without a confirmed invalidator. The default is its absence and the validity of the prayer. For this reason, if a person doubts after his prayer whether he prayed three or four rak'ahs, does it harm him? It does not harm him, because he has finished the prayer and concluded it, so it does not harm him. The second reason is that we say: He does not know now whether that impurity occurred before his taslim or after his taslim? And the default is that it did not occur. For this reason, we say: There is no repetition required of you.