Numbers 3:12
And I, behold, I have taken the Levites from among the children of Israel instead of all the firstborn that openeth the matrix among the children of Israel: therefore the Levites shall be mine;
Cross-references
Numbers 3:41 repeats the same substitution: Levites replace all firstborn males among Israel.
Numbers 3:45 reiterates the substitution: Levites are taken in place of all firstborn Israelites.
Numbers 3:40 commands a census of firstborn males, which directly leads to the substitution described here.
Numbers 8:16 confirms the same substitution: Levites are given wholly to God in place of all firstborn.
Numbers 8:18 echoes the same claim: the Levites are taken in place of every firstborn among Israel.
Numbers 18:6 gives the Levites as a gift to Aaron to serve in place of the Israelites, continuing the substitution theme.
Numbers 8:21 details the Levites' purification and wave offering, completing their consecration as substitutes.
Exodus 13:12-16 establishes the consecration of every firstborn; here the Levites are taken in their place.
Exodus 12:29 recounts the death of Egyptian firstborn, which established the principle of firstborn belonging to God—later transferred to Levites in Numbers 3:12.