I said to Ahmad: What is your opinion if one prays behind an Imam in Ramadan who is leading them in the Tarawih prayer? He said: That is permissible for the obligatory prayer. He also said in a narration by al-Marwudhi: It does not please us that one should pray the Tarawih with a group and follow them with the intention of the 'Atama (Isha) prayer. This is a branch of the issue of a person performing a mandatory prayer following one performing a supererogatory prayer, and the discussion on that has already passed.

Section: If one of the two prayers differs from the other in its actions, such as the Eclipse prayer or the Friday prayer behind someone who is praying something else, or praying other prayers behind someone who is performing these two, it is invalid according to a single narration, because this leads to differing with one's Imam in the actions, which is prohibited.

Section: Whoever prays the Fajr prayer and then doubts whether the Fajr (dawn) had risen or not, or doubts regarding a prayer he has performed, whether he performed it in its time or before it, it is incumbent upon him to repeat it, and he is permitted to lead in the repetition those who have not yet prayed. Our colleagues said: This is derived from the two narrations regarding an Imam performing a supererogatory prayer for one performing a mandatory prayer. Our view is that the basis is that the prayer remains as an obligation upon his conscience, and it is mandatory to perform it; therefore, it is valid for him to lead in it one who is performing a mandatory prayer, just as if one were to doubt: Did I pray or not? If the follower misses a rak'ah and the Imam prays five by mistake, Ibn 'Aqil said: The fifth (rak'ah) is not counted for the follower, because it (21) is a mistake and an error. The Qadi said: This rak'ah is a supererogatory one for him, but an obligatory one for the follower, so the two narrations are derived regarding this. Ahmad was asked about these issues and he refrained from answering. The better view, [if Allah wills] (22), is that it (23) is counted for him, because if it were not counted for him, it would be incumbent upon him to pray five while knowing that, and because the fifth rak'ah is mandatory for the Imam according to those who deem it obligatory to build upon certainty and when the two matters are equal in his view. Then, if it is a supererogatory act, the correct position is the validity of following him. As for his statement that it is a mistake, we say: A mistake does not prevent it from being a supererogatory act for which one is rewarded, and that is why...