What is the ruling on one who prayed 'Isha' behind an imam who prayed four consecutive rak'ahs of the night prayer without the middle tashahhud?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: I came to pray 'Isha', and it was in the month of Ramadan. He says: Then I missed the congregational prayer, but I found the imam praying the night prayer, and he prayed four rak'ahs without the middle tashahhud, so I completed it with him. The question is: What is the ruling on the prayer here, since it differed from the 'Isha' prayer in the recitation in the four rak'ahs and the lack of the middle tashahhud?

Answer:
Yes, this imam is mistaken in that he is combining. This is one of the harms of his action, that he is combining the night prayer two by two, as the Messenger (peace and blessings be upon him) said. Whoever wants the reward, the reward is in following the Sunnah. The Messenger (peace and blessings be upon him) said . This is the one who wants the reward; he follows the Sunnah. So this imam erred, and what happened resulted from his error. Also resulting from his error is a reduction in the reward. Praying two by two is more complete in reward than one who strings the prayers together. And resulting from this action is burdening the ma'mumin. If he strings the rak'ahs with them, some are sick, some are old, and some have a need, as the Prophet (peace and blessings be upon him) said . Giving the taslim every two rak'ahs is kindness to the people, so that whoever wants to leave can leave, and he does not hold them to pray eleven rak'ahs with one taslim, or more, or less. He holds the people and it is hard for them, and he does not deprive them of the prayer. He says: As long as he is doing this with us, we are praying with him, so he deprives the people of the prayer. So this is a bad action by this imam.
As for you, it is obligatory for you that on the day you prayed two rak'ahs, you sat and recited the first tashahhud. You recited the first tashahhud, then you caught up with the imam. You do not leave the first tashahhud; you sit and recite the first tashahhud, then you catch up with the imam with the intention that these last two rak'ahs are for you. Yes. Or you intend to pray alone, recite the first tashahhud, then stand and complete two rak'ahs alone, separate from the imam. This or that? Yes.