Musannaf Ibn Abi Shaybah 2621 — What those behind the imam say when he

Amir (al-Sha'bi) said: Those praying behind the imam should not say "Sami'a Allahu liman hamidah" (Allah hears the one who praises Him); rather, they should say "Allahumma rabbana laka al-hamd" (O Allah, our Lord, to You belongs all praise).