Exodus 13:15-16
15 When Pharaoh stubbornly refused to let us go, the Lord killed every firstborn male in the land of Egypt, from the firstborn of man to the firstborn of livestock. That is why I sacrifice to the Lord all the firstborn of the womb that are males, but I redeem all the firstborn of my sons.’
16 So let it be a sign on your hand and a symbol(a) on your forehead, for the Lord brought us out of Egypt by the strength of His hand.”(A)
Footnotes:
a.
Exodus 13:16: Or phylactery