Midrasch zu Schemot 8:19

And it shall be when thy son asketh thee tomorrow: “What is this?” (Exod. 13:14). Sometimes tomorrow means the next day, and sometimes it means the time to come. In the verse When thy son asketh thee tomorrow saying: “What is this?”, tomorrow means in the time to come. But the verse Tomorrow shall this sign be (Exod. 8:19) actually refers to the next day. In the verse Tomorrow will I stand upon the top of the hill (ibid. 17:9), tomorrow refers to the next day, but the verse Tomorrow your children might speak unto our children (Josh. 23:24) refers to the time to come. What is this? This refers to the laws of Passover. And it came to pass, when Pharaoh would hardly let us go (Exod. 13:15). One might understand this to mean that he became hardened of his own accord, therefore Scripture says: And the Lord hardened the heart of Pharaoh (ibid. 9:12). That the Lord slew all the firstborn (ibid. 13:15). From this they taught: The firstlings of cattle are sacrificed because of what happened to the firstborn men in Egypt, and the firstborn of man is redeemed because of what happened to the firstborn of cattle in Egypt.

Rabbi Ishmael said: The five fingers of the right hand of the Holy One, blessed be He, all of them appertain to the mystery of the Redemption. He showed the little finger of the hand to Noah, (pointing out) how to make the ark, as it is said, "And this is how thou shalt make it" (Gen. 6:15). With the second finger, which is next to the little one, He smote the firstborn of the Egyptians, as it is said, "The magicians said unto Pharaoh, || This is the finger of God" (Ex. 8:19). With how many (plagues) were they smitten with the finger? With ten plagues. With the third finger, which is the third (starting from) the little finger, He wrote the tables (of the Law), as it is said, "And he gave unto Moses, when he had made an end of communing with him… tables of stone, written with the finger of God" (Ex. 31:18). With the fourth finger, which is next to the thumb, the Holy One, blessed be He, showed to Moses what the children of Israel should give for the redemption of their souls, as it is said, "This they shall give… half a shekel for an offering to the Lord" (Ex. 30:18). With the thumb and all the hand the Holy One, blessed be He, will smite in the future all the children of Esau, for they are His foes, and likewise (will He smite) the children of Ishmael, for they are His enemies, as it is said, "Let thine hand be lifted up above thine adversaries, and let all thine enemies be cut off" (Mic. 5:9).