Les Nombres 19:9 Halakha : Mishneh Torah, Overview, Mishneh Torah, Red Heifer, Mishneh Torah, Positive Mitzvot & Sefer HaChinukh

LAWS CONCERNING THE RED HEIFER.
These comprise two affirmative precepts: 1) the Red Heifer; 2) the uncleanliness of the waters of sprinkling (Num. 19:9-22) and of the mode in which these are to be used for purification.

12. Everyone's word is accepted with regard to the ritual purity of articles and persons involved in this purification process, even that of the common people. The rationale is that because of all the stringencies and extra measures applied to it, everyone is careful with regard to it. This is alluded to in the Torah which states Numbers 19:9: "And it will be for the congregation of Israel for safekeeping." Implied is that all of Israel are fit for its safekeeping. Therefore if a common person brings an earthenware container from his home and says: "This container is pure for the purification process involving the ashes of the red heifer," it is considered as pure. Water may be sanctified in it and sprinkled from it even though this container would be considered as impure for sacrificial foods and for terumah. Similarly, if a common person says: "I have purified myself for the purification process involving the ashes of the red heifer" or the water for this process was in his possession and he says that it is pure, his word is accepted. For no Jewish person treats this purification process lightly.

That the leper shall shave all his hair, as it is said, “But it shall be on the seventh day, that he shall shave all his hair” (Lev. 14:9).