Sahih Ibn Khuzaymah

It is narrated from Sayyiduna Ali (may Allah be pleased with him) that when the Noble Prophet (peace and blessings be upon him) would begin the prayer, he would say « اللهُ أَكْبَرُ ». (Both of the honorable teachers of the Imam) narrated a part of the hadith and said that when the Prophet (peace and blessings be upon him) would raise his head from bowing (ruku‘), he would recite this supplication « سَمِعَ اللهُ لِمَنْ حَمِدَهُ ، رَبَّنَا وَلَكَ الحَمْدُ ، مِلْءَ السَّمواتِ والأرضِ، ومِلْءَ ما شِئتَ مِن شيءٍ بعدُ »: “Allah has heard the one who praised Him. O our Lord, to You belongs all praise, filling the heavens, filling the earth, and filling whatever else You will after that (all praise is Yours).”