For the Scripture says, "You shall not muzzle the ox when it treads out the grain." And, "The laborer is worthy of his wages."
And, The laborer is worthy of his hire ... There is absolutely no doubt that Paul here classified this second quotation as "Scripture," to which he attributed both this remark and the one from Deuteronomy.  But, where is this Scripture?  It is certainly not in the Old Testament.  It is in the New Testament: