Musannaf Ibn Abi Shayba 3:466

Ghundar narrated to us, from Shu'bah, from Muhammad ibn Abd al-Rahman al-Ansari, who said: I heard Abd al-Rahman al-A'raj say: I prayed with Abu Hurayrah. When he said the takbir, he remained silent for a moment, then he said: "Al-hamdu lillahi rabbil-'alamin" (Praise be to Allah, Lord of the worlds).