On the sixth day of the week, something unprecedented happened with the manna. (Exodus 16:22) records that the Israelites gathered a double portion, two omers instead of the usual one. Rabbi Yehoshua confirmed that this was the "doubled bread," the special provision for the coming Sabbath when no manna would fall.
But the more revealing moment came when the princes of the congregation approached Moses. The leaders of Israel came to their teacher with a question that would echo through Jewish history for thousands of years: "Why is this day different from all the other days?"
The phrasing is unmistakable. Centuries later, the same question structure would become the opening of the Four Questions asked at the Passover Seder: "Mah nishtanah halailah hazeh," why is this night different from all other nights? But here in the wilderness, the question was asked for the first time, not about Passover but about Shabbat (the Sabbath). The princes noticed that the sixth day produced double manna, something that had never happened before, and they wanted to know why.
The Mekhilta DeRabbi Yishmael preserves this moment as the very first "mah nishtanah" in Jewish tradition. Before there was a Seder, before there was a Haggadah (non-legal rabbinic narrative), before the Four Questions were formalized, the princes of Israel stood before Moses in the desert and asked the original version of the question that Jewish children would still be asking thousands of years later. The answer Moses gave them was the Sabbath itself, the day that God set apart from the beginning of creation.