Midrash su Giosuè 22:24

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.

(Exodus 13:14) "And it shall be if your son asks you tomorrow": "tomorrow" may indicate" in the present," and it may indicate "in time to come." (Exodus 17:9) "Tomorrow I will stand on top of the hill" — in the present. (Joshua 22:24) "Tomorrow your children might say to our children" — in time to come. (It is written, Devarim 6:20) "If your son asks you tomorrow (i.e., in the time to come): What are the testimonies and the statutes, etc.": There are four sons: a wise son, a wicked son, a simple son, and one who does not know how to ask. What does the wise son say? "What are the testimonies and the statutes and the judgments that the L-rd our G-d commanded us?" — you, likewise, "open" to him in the halachoth of Pesach — "ein maftirin achar hapesach afikoman." What does the wicked son say? (Exodus 12:26) "What is this (Pesach) service to you?" "to you" and not to him. Because he disassociated himself from the congregation and denied the foundation (of the faith), you, likewise, blunt his teeth and tell him (Ibid. 13;8) "Because of this (the mitzvoth) the L-rd wrought for me when I went out of Egypt." For me and not for you. Had you been there, you would not have been redeemed. What does the simple son say? (Ibid. 14) "What is this?" And you shall tell him (Ibid.) "With might of hand did the L-rd take us out of Egypt from the house of bondage." And he who does not know how to ask, you open for him, as it is written (Ibid. 8) "And you shall tell your son on that day, etc." Variantly: "What are the testimonies and the statutes, etc.": R. Eliezer says: Whence is it derived that if there were a company of sages or of disciples they must occupy themselves with the halachoth of Pesach until midnight? From "What are the testimonies, etc."