Canon 7 issued by the Tenth Council of Toledo [Spain] [Unconfirmed]
Commentary from other sources:
1) “…on December 1, 656, at [Tenth Council of] Toledo…[Canon] 7. It was loudly complained that clerics sell Christian slaves to Jews, and this was entirely forbidden, with the quotation of many passages from the Bible.”
Karl Joseph von Hefele: “A History of the councils of the church, from the original documents. By the Right Rev. Charles Joseph Hefele.” (1895) pp. 474-475