Midrash sa Exodo 21:21: Mekhilta DeRabbi Yishmael

R. Eliezer says: Scripture speaks of a Canaanite (as opposed to a Hebrew) man-servant. You say this, but perhaps it speaks of a Hebrew? (This is not so, for) it is written here "his man-servant or his maid-servant," and elsewhere, (Leviticus 25:44) "From them (the Canaanites) shall you buy a man-servant or a maid-servant." Just as there, the Torah speaks of the Canaanites, so, here. Variantly: man-servant is being likened to maid-servant, and maid-servant to man-servant. Just as "maid-servant" — (she may be sold as a maid-servant,) whether adult or minor, so "man-servant," adult or minor — to exclude a Hebrew man-servant, who although (he may be sold as) a man-servant when he is an adult, may not (be sold as) a man-servant when he is a minor. And to exclude a Hebrew maid-servant, who, although she may be a maid-servant when she is a minor, may not be a maid-servant when she is an adult, (leaving her master, as she does, with the advent of pubertal signs.) R. Yitzchak said: I might understand that (also included is) a servant of two partners or one who is half-free, half-slave; it is, therefore, written "his man-servant or his maid-servant." Just as the first implies a servant that is entirely his, so, the second — to exclude the servant of two partners or one that is half-free (half-slave). R. Yishmael says: Scripture speaks of a Canaanite man-servant, it being written (Exodus 21:21) "for he (the servant) is his money." Just as his money is his for all time and he exercises complete control over it, (so, the servant being spoken of) — to exclude a Hebrew man-servant, who, though under his complete control, is not his for all time, (leaving, as he does in Yovel), and to exclude a servant of two partners or one who is half-free (half-slave), who, though he is his for all time, is not under his complete control.

Now if (in the killing of) an Israelite, the graver (instance), not being subject to (the provision of [Exodus 21:21]) "But if one or two days," he is not liable unless it be with an implement of killing potential and in a locus which is critical to life, then (in the killing of) a Canaanite, the instance of lesser gravity, being subject to the above provision, how much more so should he not be liable unless it be with an implement of killing potential and in a locus which is critical to life! (Why, then, need it be written?) For if you say this, you have ruled for punishment through a fortiori reasoning, wherefore it is written "with a rod, etc.", to teach that punishment is not to be ruled for through such reasoning.

(Exodus 21:21) "But if one day or two days": I understand this literally. It is, therefore, (i.e., negating this,) written "if one day": How (are these two verses to be reconciled?) One day which is like two days; two days which are like one day. How so? A twenty-four hour period.