A Treatise on the Law and the Gospel, ch. VII, "Of the Difference between the Law and the Gospel" (Edinburgh: Ogle, Allardice and Thomson, 1819), p. 173

In the affair of justification, the law as a covenant of works, is not only to be distinguished, but to be separated from the gospel. When a true believer is, at any time, in doubt of his justification and title to etern…