Musannaf Ibn Abi Shayba 13:1005

Abu Bakr narrated to us, he said: Yahya bin Sa’id narrated to us, from Salih bin Muslim, he said: I asked al-Sha’bi about purchasing the surplus in the stipend (al-’ata’). He said: "I do not command it, nor do I forbid it, but I forbid it for myself and my children, and those who are better than me have done it." I said: "Who?" He said: "The Commander of the Faithful."