Hazrat Abu Huraira (may Allah be pleased with him) says that in terms of prayer, I am the most similar to the Prophet (peace and blessings of Allah be upon him) among you all. When the Prophet (peace and blessings of Allah be upon him) said "Sami' Allahu liman hamidah," he would say "Rabbana wa lakal hamd." When he went into bowing (ruku'), or raised his head from bowing, or stood up for the second rak'ah, at every occasion he would say the takbeer.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 8253