Ramban on Exodus 13:12/רמב"ן על שמות י״ג:י״ב

1V’HA’AVARTA’ UNTO THE ETERNAL ALL THAT OPENETH THE WOMB. This is an expression of setting apart, i.e., that one is to remove the firstling from the flock and it is to be for the Eternal. Then He reverts and explains that this “setting apart” means that every first male offspring dropped by a beast, and every first offspring of an ass and every firstborn son of a man shall be the Eternal’s. But Rashi commented: “And thou shalt set apart unto the Eternal all that openeth the womb. Scripture is speaking of the firstborn of man.”