Jami` at-Tirmidhi 267
جامع الترمذي#267SahihAbu Hurairah narrated that :Allah's Messenger said: "When the Imam says: (Sami Allahu liman hamidah) 'Allah listens to those who praise Him. Then (all of you) say: (Rabbana wa lakal-hamd) 'O our Lord! And to You is the praise for whoever's saying concurs with the saying of the angels, then his past sins will be forgiven
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 2:119