Musnad Ahmad 788:181

Yahya ibn Sa'id narrated to us, Hisham narrated to us, he said: Qatadah narrated to us, from Yunus ibn Jubayr, from Hattan ibn 'Abd Allah al-Raqashi, that al-Ash'ari prayed with his companions. A man from the people said, when he sat in his prayer: "Prayer has been established with righteousness and zakat." When al-Ash'ari finished his prayer, he turned to the people and said: "Which of you said such-and-such a word?" The people remained silent. He said: "Abu 'Abd al-Rahman." My father said: "Arrama" means silence. He said: "Perhaps you said it, Hattan?" Hattan ibn 'Abd Allah said: "By Allah, I did not say it, and I feared that you would rebuke me for it." A man from the people said: "I said it, and I intended nothing by it but good." Al-Ash'ari said: "Do you not know what you say in your prayer? For the Prophet of Allah, peace and blessings of Allah be upon him, addressed us and taught us our Sunnah, and explained our prayer to us. He said: 'Straighten your rows, then let the one among you who is most proficient in recitation lead you. When he says the takbir, say the takbir. And when he says: {Not of those who are astray} [Al-Fatiha: 7], say: Amin, and Allah will answer you. When the Imam says the takbir and bows, say the takbir and bow, for the Imam bows before you and rises before you.'" The Prophet of Allah, peace and blessings of Allah be upon him, said: "That is for that." "When he says: 'Allah hears those who praise Him,' say: 'O Allah, our Lord, to You be the praise,' and Allah will hear you. For Allah, the Mighty and Majestic, said upon the tongue of His Prophet, peace and blessings of Allah be upon him: 'Allah hears those who praise Him.' When the Imam says the takbir and prostrates, say the takbir and prostrate, for the Imam prostrates before you and rises before you." The Prophet of Allah, peace and blessings of Allah be upon him, said: "That is for that." "When he is at the sitting, let the first thing one of you says be: 'The greetings, the good things, and the prayers are for Allah. Peace be upon you, O Prophet, and the mercy of Allah and His blessings. Peace be upon us and upon the righteous servants of Allah. I bear witness that there is no god but Allah, and that Muhammad is His servant and His messenger.'"