To what extent is it true that the phrase "Rabbana wa lakal-hamd" (Our Lord, to You be all praise) after the Imam says "Sami'a Allahu liman hamidah" (Allah hears those who praise Him) did not exist during the time of the Prophet, peace and blessings be upon him, and that it came later?

The statement that the Companions did not say "Rabbana wa lakal-hamd" (Our Lord, and to You be all praise) after rising from bowing is false. It has been proven that they did say it, and that the Prophet, peace and blessings be upon him, commanded them to do so. In al-Bukhari, from Rifa’ah ibn Rafi’ al-Zuraqi, he said: "I prayed behind the Prophet, peace and blessings be upon him. When he raised his head from the bowing, he said: 'Sami’a Allahu liman hamidah' (Allah hears the one who praises Him). A man behind him said: 'Rabbana wa lakal-hamd, hamdan kathiran tayyiban mubarakan fih' (Our Lord, and to You be all praise, abundant, good, and blessed praise). When he finished [the prayer], he asked: 'Who was the speaker?' He said: 'I was.' He [the Prophet] said: 'I saw more than thirty angels competing as to which of them would record it first.'" And in al-Bukhari and Muslim, the Prophet, peace and blessings be upon him, said: "When the Imam says: 'Sami’a Allahu liman hamidah,' then say: 'Allahumma Rabbana lakal-hamd' (O Allah, our Lord, to You be all praise)." Therefore, the statement that this phrase was innovated after the era of the Prophet, peace and blessings be upon him, is incorrect, and the sound, clear Sunnah is to the contrary.