Maliks Muwatta Book 3, Hadith Number 20.
Section : The Opening of the Prayer.
Yahya related to me from Malik from Ibn Shihab from Abu Salama ibn Abdar-Rahman ibn Awf that Abu Hurayra used to lead them in prayer and would say “Allah is greater” whenever he lowered himself and raised himself. When he had finished he would say, “By Allah, I am the person whose prayer most resembles the prayer of the Messenger of Allah, may Allah bless him and grant him peace.”