Exodus 12:14

לזכרון [AND THIS DAY SHALL BE UNTO YOU] FOR A MEMORIAL — in future generations (i. e. in the future). וחגתם אתו AND YE SHALL CELEBRATE IT AS A FEAST— Scripture states: the day that is to serve you as a memorial, that day thou shalt celebrate as a feast, but we have not yet heard which is the day that is to be a memorial; therefore Scripture says (Exodus 13:3) “Remember (זכור) this day in which ye went out” and this teaches us that the day of the Exodus itself is the day which is to be the memorial (זכרון). Now, on which day did they go forth? Scripture states, (Numbers 33:3) “On the morrow after the Passover-sacrifice they went forth”. Thus you must say that the day of the fifteenth of Nisan is that of the Feast, for on the night of the fifteenth (i. e. what we would term the night following the day of the fourteenth) they ate the Passover-sacrifice, and consequently on the next morning they went forth (Mekhilta). לדרתיכם וגו׳ [YE SHALL CELEBRATE IT] FOR YOUR GENERATIONS etc. — I might understand from this that it need be celebrated only for the minimum of a plurality of generations, viz., two; therefore Scripture goes on to state “an ordinance for ever shall ye celebrate it as feast” (Mekhilta).

And this day shall be to you for a memorial; and you shall keep it a feast to the Lord; throughout your generations shall you keep it a feast by ordinance for ever.

וְהָיָה֩ הַיּ֨וֹם הַזֶּ֤ה לָכֶם֙ לְזִכָּר֔וֹן וְחַגֹּתֶ֥ם אֹת֖וֹ חַ֣ג לַֽיהֹוָ֑ה לְדֹרֹ֣תֵיכֶ֔ם חֻקַּ֥ת עוֹלָ֖ם תְּחׇגֻּֽהוּ׃