Musannaf Ibn Abi Shayba 28:802

Ismail ibn Ayyash narrated to us, from Asad ibn Abd al-Rahman al-Khath'ami, from Muqbil ibn Abd Allah, from Hani ibn Kulthum al-Kinani, who said: I was the chamberlain of the army that conquered the Levant. I wrote to Umar: "We have conquered a land with much food and fodder, and I disliked proceeding with anything of that except by your command and permission, so write to me with your command regarding that." Umar wrote to me: "Let the people eat and provide fodder. Whoever sells anything for gold or silver, then the fifth of Allah and the shares of the Muslims have become due upon it."