Substitution during the prayer

Q: I went to the mosque for the 'Isha' prayer and found that the congregation had gotten ahead of me by two rak'ahs. After I said the takbir to join the prayer, the imam had an excuse that caused him to break off the prayer and appoint me as the imam in his place. What should I do in this situation, given that I am behind by two rak'ahs?

A: You must pray the two rak'ahs that you caught up with, and sit for the first tashahhud, which is for you, while it is the final tashahhud for the ma'mums. It is better that you send blessings upon the Prophet (peace and blessings be upon him), then stand up and gesture to them to sit down until you have finished making up the two rak'ahs, and then say the taslim with them all. This is because you are excused in this situation, and they are excused, and they must wait for you. This is what is obligatory for all of you. If he had appointed someone who had not missed any part of the prayer, that would have been more appropriate. And success is from Allah.