Musannaf Ibn Abi Shayba 27:333

Sharik narrated to us, from al-Ash'ath, from al-Aswad ibn Hilal, that a Bedouin from among them said: I witnessed the morning prayer with the Prophet, may Allah bless him and grant him peace, one day. He turned to the people with his face and said: "I saw people from my nation last night being weighed. So Abu Bakr was weighed and he outweighed, then Umar was weighed and he outweighed."