Numbers 8:17-18

8:17 For all the firstborn males among the Israelites are mine, both humans and animals; when I destroyed ¹  all the firstborn in the land of Egypt I set them apart for myself. 8:18 So I have taken the Levites instead of all the firstborn sons among the Israelites.

[8:17]  ¹ tn The idiomatic “on the day of” precedes the infinitive construct of נָכָה (nakhah) to form the temporal clause: “in the day of my striking…” becomes “when I struck.”