EXO 13:15

15 And it came to pass, when Pharaoh stubbornly refused to let us go, that Hashem killed kol bechor of Eretz Mitzrayim, both the bechor adam, and the bechor behemah; therefore Ani zovei'ach laHashem[(I sacrifice to Hashem)] kol that openeth the rechem [(womb)], being hazecharim [(the males)]; but kol bechor of my banim I redeem.