EXO 12:13

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.