Musannaf Ibn Abi Shayba 18:411

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Zayd ibn Aslam, from Muslim ibn Jundub, from Aslam, the freed slave of Umar, he said: I heard Umar on the pulpit saying: "Regarding the rib, [the compensation is] a camel."