The commandment of the impurity of a dead body: That we were commanded regarding the matter of impurity from a dead body to behave as the Torah commanded us about it, as it is stated (Numbers 19:14), “This is the law; a man who dies in a tent — anyone who comes into the tent and everything that is in the tent will become impure seven days.”

And I have written what I could from the roots of the matter of the impurity of the dead body in the Order of Emor el HaKohanim (Sefer HaChinukh 263); and so too, some of the laws — as is my custom — take it from there. And all the laws of the one rendered impure by a dead body are elucidated in Tractate Ohalot. (See Mishneh Torah, Laws of Defilement by a Corpse 1.) And in the Order of Vayehi Bayom Hashmini in the commandment of the impurity of the eight crawling animals (Sefer HaChinukh 159), you will also see it written that Ramban, may his memory be blessed, disagrees with Rambam, may his memory be blessed, not to count all the laws of the impurities in the tally of the commandments — and his reasoning is with him.