Musannaf Ibn Abi Shayba 28:353

Ghassan ibn Mudar narrated to us, from Sa'id ibn Yazid, from Abu Nadra, from Jabir, who said: When Umar assumed the Caliphate, he established the obligatory shares (fara'id), organized the registers (diwans), and appointed the overseers (urafa'). Jabir said: So he appointed me as an overseer over my companions.