Shemoth (Exodus) 12:12-13

‘And I shall pass through the land of Mitsrayim on that night, and shall strike all the first-born in the land of Mitsrayim, both man and beast. And on all the mighty ones of Mitsrayim I shall execute judgment. I am יהוה. ‘And the blood shall be a sign for you on the houses where you are. And when I see the blood, I shall pass over you, and let the plague not come on you to destroy you when I strike the land of Mitsrayim.