If one catches the imam in ruku', sujud, or sitting, does he say takbir for entering prayer and for moving, or only for entering prayer?

Question:
May Allah reward you. The questioner, Ahmad Mushay al-Butri, asks in his third question: When a person arrives and the imam is in ruku', does he say takbir twice—one for entering prayer and one for ruku'—or is one sufficient? And if he arrives and the imam is in sujud or sitting, what does he do?

Answer:
Yes. If one catches the imam in ruku', he must say the takbir for entering prayer while standing, then lower himself into ruku' with a second takbir, which is the takbir for moving. In this case, this takbir is a recommended practice (sunnah); whoever does it earns reward, and whoever leaves it out has done nothing wrong. However, the takbir for entering prayer is obligatory, and it must be done while standing. As for the one who arrives and the imam is sitting or in sujud, he follows him: he says the takbir for entering prayer while standing, then sits with the imam or prostrates with him if he catches him in sujud, in order to obtain the reward of following. This is based on the saying of the Messenger (peace and blessings be upon him): "Whoever arrives and the imam is in a certain state, let him be with him in that state." Yes. The takbir for entering prayer is sufficient. Yes, the stability of the prayer is sufficient for him.