It is narrated from Abu Ishaq: Abdullah bin Yazid (may Allah be pleased with him) narrated to me the hadith of al-Bara' (may Allah be pleased with him), and he was truthful, that they used to pray behind the Messenger of Allah (peace and blessings be upon him). When he (peace and blessings be upon him) raised his blessed head from bowing, no one would bend his back until the Messenger of Allah (peace and blessings be upon him) had placed his forehead on the ground; then those following him (peace and blessings be upon him) would go into prostration.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2596