וַיְהִ֗י כִּֽי־הִקְשָׁ֣ה פַרְעֹה֮ לְשַׁלְּחֵנוּ֒ וַיַּהֲרֹ֨ג יְהֹוָ֤ה כָּל־בְּכוֹר֙ בְּאֶ֣רֶץ מִצְרַ֔יִם מִבְּכֹ֥ר אָדָ֖ם וְעַד־בְּכ֣וֹר בְּהֵמָ֑ה עַל־כֵּן֩ אֲנִ֨י זֹבֵ֜חַ לַֽיהוָ֗ה כָּל־פֶּ֤טֶר רֶ֙חֶם֙ הַזְּכָרִ֔ים וְכָל־בְּכ֥וֹר בָּנַ֖י אֶפְדֶּֽה׃
and it came to pass, when Pharaoh would hardly let us go that the LORD slew all the firstborn in the land of Egypt, both the first-born of man, and the first-born of beast; therefore I sacrifice to the LORD all that openeth the womb, being males; but all the first-born of my sons I redeem.
Related passages and parallel verses for Exodus 13:15.