וְכָל־פֶּ֤טֶר חֲמֹר֙ תִּפְדֶּ֣ה בְשֶׂ֔ה וְאִם־לֹ֥א תִפְדֶּ֖ה וַעֲרַפְתּ֑וֹ וְכֹ֨ל בְּכ֥וֹר אָדָ֛ם בְּבָנֶ֖יךָ תִּפְדֶּֽה׃
And every firstling of an ass thou shalt redeem with a lamb; and if thou wilt not redeem it, then thou shalt break its neck; and all the first-born of man among thy sons shalt thou redeem.
Read kabbalistic (mystical) interpretation of Exodus 13:13: and classical mystical sources.