Exodus 21:21 - Ellicott's Commentary On The Whole Bible

If he continue a day or two, he shall not be punished. — Comp. the proviso with respect to freemen (Exodus 21:19). The notion is, that unless the death follows speedily it must be presumed not to have been intended; and this might be especially presumed in the case of a man killing his slave, since thereby he inflicted on himself a pecuniary loss.