Shemot 12:13

Orthodox Jewish Bible

¹³ And the dahm shall be for you, an ot (sign) upon the batim (houses) where ye are; and when I see the dahm, oofasachti (then I will pass over, skip, spare) you [plural], and the negef (plague, blow, striking, i.e., death of firstborn) shall not be upon you to destroy you, when I strike fatally with a blow against Eretz Mitzrayim.