Charles Ellicott Commentary 2 Samuel 12:6

"and he shall restore the lamb fourfold, because he did this thing, and because he had no pity." — 2 Samuel 12:6 (ASV)

Fourfold. —In exact accordance with the Law (Exodus 22:1). The Septuagint (in most copies “sevenfold,” compare to Proverbs 6:31) and the Chaldee (“fortyfold”) have expressed more of human indignation; but David knew the Law too well to change its terms.