Rollock, Robert – ‘Of the Word of God, or of the Covenant in General, and of the Covenant of Works in Special’ †1599 5 pp. being ch. 2 of A Treatise of Effectual Calling, chapters 3-5 are also relevant.
Berkhof, Louis – Man in the Covenant of Works, HTML, 1949, 19 paragraphs from his Systematic Theology
On the Histoical Origin of the Covenant of Works
Foord, Marty – The Covenant of Works Pre-Reformation, 2014, 4 paragraphs, blog post
Foord has found a proto-Covenant-of-Works in Gregory the Great’s (540-604) Moralia on Job and in Boethius’ (480-524/5) De Fide Catholica. The latter quote is given in full.