Reference for Numbers 8:18

וָאֶקַּח֙ אֶת־הַלְוִיִּ֔ם תַּ֥חַת כָּל־בְּכ֖וֹר בִּבְנֵ֥י יִשְׂרָאֵֽל׃

And I have taken the Levites instead of all the first-born among the children of Israel.

BDB