Catching two rak'ahs with the imam in a mosque after the obligatory prayer, and leading the one who is unable to prostrate

The questioner:
Honorable Shaykh, if I have prayed the obligatory prayer in one mosque, and I go to another mosque and find it full, and I catch two rak'ahs of the prayer, is it permissible for me to say the closing salam when the imam says it, or should I complete the prayer?

The Shaykh:
Follow the imam, pray the imam's prayer. The Messenger of Allah (peace and blessings be upon him) said: So follow him and complete the prayer, and it will be a voluntary prayer.

The questioner:
And the other case is if the imam's prostration is like his bowing, because he is unable to perform it properly, then leave him and lead the people in that.

The Shaykh:
Okay.

The questioner:
If his prostration is like his bowing, because he is unable to bow down to it, what did his father know about that?

The Shaykh:
I mean he is unable to prostrate on the ground; the imam is unable to prostrate on the ground. It is not befitting for him to lead the people in prayer because he is unable to perform one of the pillars of the prayer, which is prostrating on the seven limbs. So he should pray as a follower and not as an imam, because he is unable to perform one of the pillars of the prayer.