Musannaf Ibn Abi Shayba 28:444

'Utham ibn 'Ali narrated to us, from al-A'mash, from Abu Ishaq, from Ibn Mudrib, who said: 'Umar divided the Sawad among the people of Kufa, and each man among them received three farmers. 'Umar said to him, "And who will be for them after them?" So he left them.