Musannaf Ibn Abi Shayba 27:290

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