Mishkat al-Masabih

Abu Musa al-Ash‘ari reported God’s Messenger as saying:When you pray make your rows straight and let one of your number act as your imam. If you say the takbir when he says it and say Amen when he says “Not of those with whom Thou art angry nor of those who go astray”, God will accept your prayer. When he says the takbir and bows, say it and bow, for the imam bows before you and raises himself before you. Then God’s Messenger said, “The one is equivalent to the other.”* And he said: If you say, “O God our Lord, to Thee be the praise,” when he says, “God listens to him who praises him,” God will listen to you. * Although the imam begins and ends his bowing before you do, your bow lasts the same length of time as his. Muslim transmitted it.