Sidna Abu Hurairah, may Allah be pleased with him, says that the Messenger of Allah, peace and blessings be upon him, used to teach us and say: Do not do any action before the Imam; when he says the takbeer, then you say the takbeer; and when he says "wa la ad-dallin," then you say "Ameen" after him; and when he bows (for ruku‘), then you bow after him; and when he says "Sami‘ Allahu liman hamidah," then you say "Rabbana lakal hamd" after him.