Abu Huraira reported God’s Messenger as saying, “The imam is appointed only to be followed, so when he says the takbir, say it also; and when he recites, listen silently.”
Ibn ‘Umar and al-Bayadi reported God’s Messenger as saying, “He who prays holds intimate converse with his Lord, so he must consider how he does so, and none of you must recite the Qur’an more loudly than others.
‘Abdallah b. Abu Aufa told of a man who came to the Prophet and said, “I am unable to learn any of the Qur’an, so teach me something which will suffice me.” He told him to say, “Glory be to God; Praise be to God; There is no god but God; God is most great; There is no might and no power except in God.” He said, “Messenger of God, this is for God; but what is there for me?” He told him to say, “O God, have mercy on me, heal me, guide me, and provide for me.” He said that the man clenched his hands, whereupon God’s Messenger said, “This man has filled his hands with good.”
Abu Dawud transmitted it, and Nasa’i’s transmission finished with “except in God.”
Abu Huraira said that when God’s Messenger had finished a prayer in which he had recited aloud, he asked, “Did any of you recite along with me just now?” When a man replied that he had, he said, “I am wondering what is the matter with me that I should be contended with regarding the Qur’an.” He said that when the people heard that from God’s Messenger they ceased reciting along with him the passages which he recited aloud in the prayers.
Malik, Ahmad, Abu Dawud, Tirmidhi, and Nasa'i transmitted it, and Ibn Majah transmitted something similar.