It is narrated from the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), that the Messenger of Allah (peace and blessings be upon him) used to begin the prayer with the takbir. Then the full hadith was mentioned, and in it there is also: When he (peace and blessings be upon him) bowed, he would hold his head neither too high nor too low, but level. Then the full hadith was mentioned.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2552