Musannaf Ibn Abi Shaybah

Hazrat Abu Huraira narrates that the Noble Prophet (peace and blessings be upon him) said: The imam is appointed to be followed, so when he says the takbeer, you say the takbeer, and when the imam recites, you remain silent, and when the imam says { غَیْرِ الْمَغْضُوبِ عَلَیْہِمْ ، وَلاَ الضَّالِّینَ }, you should say Ameen. And when the imam bows (for ruku), you bow, and when the imam says "Sami' Allahu liman hamidah," you say, "Allahumma Rabbana wa lakal hamd." And when the imam prostrates, you prostrate. And when the imam prays sitting, you pray sitting. And it has been mentioned from (Imam) Abu Hanifa that: if the imam is sitting, following him (by sitting) is not correct.