Abu Dawud

1؎: In the hadith of «مسئ صلاۃ» regarding the teaching of prayer, the Messenger of Allah (sallallahu alayhi wa sallam), while raising his back from bowing (ruku‘), used to recite: «سمع الله لمن حمده». The Prophet (sallallahu alayhi wa sallam) said: A man's prayer is not complete until he does this and this. In this hadith, it is mentioned that then he should bow (ruku‘), then say: «سمع الله لمن حمده» until he stands up straight (Abu Dawud). After that, while in the standing position (qiyam), the Prophet (sallallahu alayhi wa sallam) would recite «ربنا ولك الحمد». The Prophet (sallallahu alayhi wa sallam) gave this command to both the imam and the follower by saying: «صلوا كما رأيتموني أصلي». The Prophet (sallallahu alayhi wa sallam) used to say: The imam has only been appointed to be followed. He said: And when the imam says «سمع الله لمن حمده», then you should say «اللہم ربنا ولک الحمد». And its reasoning has been explained in another hadith in this way: Whoever's statement coincides with that of the angels, his past sins will be forgiven. According to this detail, both the imam and the follower should recite both supplications. Some imams, such as Sha‘bi, hold the view that the follower should not say «سمع الله لمن حمده», but suffice with «ربنا ولك الحمد» only.