Numbers 15:24-26

Then it shall be, if ought be committed by ignorance without the knowledge of the congregation, that all the congregation shall offer one young bullock for a burnt offering, for a sweet savour unto the LORD, with his meat offering, and his drink offering, according to the manner, and one kid of the goats for a sin offering.

If ought be committed by ignorance. The Mosaic ritual was complicated, and the ceremonies to be gone through in the various instances of purification which are specified, would expose a worshipper, through ignorance, to the risk of omitting or neglecting some of them. This law included the stranger in the number of those for whom the sacrifice was offered for the sin of general ignorance.