Musannaf Ibn Abi Shayba 24:127

Ibn ‘Ulayyah narrated to us, from Hisham, from al-Hasan, who said: Ziyad wrote to al-Hakam ibn ‘Amr al-Ghifari while he was over Khurasan, saying: "The Commander of the Faithful has written [ordering] that you select for him the white [silver] and the yellow [gold], and that you do not distribute gold or silver among the people." He wrote back to him: "Your letter reached me, in which you mention that the Commander of the Faithful has written [ordering] that you select for him the white and the yellow. And I have found the Book of Allah before the letter of the Commander of the Faithful. And by Allah, if the heavens and the earth were closed up against a servant, then he feared Allah, Allah would make for him a way out. And peace be upon you." Then he said to the people: "Go forth to your wealth." So they went forth, and he distributed it among them.