What is the ruling on delaying joining the imam until he bows?

Question : The questioner asks: What is your opinion of the one who prays tarawih or the night prayer, and sits until the imam says the takbir for bowing, then he stands and bows with him? Is his action sound? And is it permissible for a person to say the takbir while sitting, so that when the imam bows, he stands and bows with him and prostrates, then returns to sit again and does the same?

Answer : Yes. As for a person delaying joining the imam until he says the takbir for bowing, this action is not sound. In fact, I hesitate as to whether his bowing is valid or not.
Why? Because he intentionally delayed to the point where he could not recite al-Fatihah. Reciting al-Fatihah is a pillar that is not dropped for the imam, the ma'mum, or the one praying alone. So for him to remain until the imam bows, then stand and bow with him, this is a mistake without doubt, and it endangers his prayer, or at least his bowing, such that he may not have caught it. As for his saying the takbir with the imam while sitting, and when he is about to bow, he stands and bows, there is no harm in that. The Prophet (peace and blessings be upon him), when he was old and heavy, used to do this. That is, he would start while sitting and recite, and when he was about to bow, he would stand and recite whatever he could of the Qur'an, then bow. Likewise, if he bows with the imam, then the imam stands for the second rak'ah and he sits, and when the imam is about to bow in the second rak'ah, he stands and bows with him. All of this is without harm.