Musannaf Ibn Abi Shayba 13:3425

Abu Bakr narrated to us, he said: Isa ibn Yunus narrated to us, from Salih ibn Abi al-Akhdar, from al-Walid ibn Abi Hisham, from Malik ibn Abd Allah al-Khath'ami, who said: We were sitting with Uthman, and he said: "Who is here from the people of al-Sham?" So I stood up. He said: "Convey to Mu'awiyah that when he acquires spoils of war, he should take five shares, and let him write on each share of them 'For Allah', then let him cast lots. So wherever it falls, he should take it."