It is narrated from Ibn Shihab (may Allah have mercy on him): Abu Bakr bin Abd al-Rahman bin al-Harith bin Hisham (may Allah have mercy on him) narrated to me that he heard Abu Hurayrah (may Allah be pleased with him) say: The Messenger of Allah (peace and blessings be upon him) used to, and then he mentioned the complete hadith. In it there is also that he (peace and blessings be upon him) "would say the takbir while going down for prostration."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2627