Rebbi — Rabbi Yehudah HaNasi, the redactor of the Mishnah (the earliest code of rabbinic law) and the most authoritative sage of his generation — weighs in on the Passover cooking prohibition with a reading that adds a dimension neither Rabbi Yishmael nor Rabbi Akiva addressed. His concern is not which liquids are forbidden, but when the prohibition applies.
The Torah says, "Eat of it only roasted in fire" (Exodus 12:9). Rebbi observes that this command specifically governs the nighttime eating of the Pesach (Passover). The lamb must be eaten roasted, at night, as part of the seder meal. That much is clear. But what about the daytime?
During the day of the fourteenth of Nissan, there is no commandment to eat the Passover lamb — the eating happens after dark. So one might logically conclude that the prohibition against eating it raw or cooked only applies when the positive commandment to eat it roasted is in effect. During the day, when no eating is commanded, perhaps no method of preparation is forbidden either.
Rebbi rejects this reasoning. The doubled phrase "uvashel mevushal" carries the connotation of "whenever it is cooked" — at any time, day or night. The prohibition is not tied to the moment of commanded eating. It is absolute. From the instant the Pesach lamb is designated for the offering, it may not be prepared in any way other than roasting over fire. The doubling in the Torah's language extends the prohibition across the entire timeline, not just the evening meal.
This ruling has a practical consequence: even during the day, before the seder begins, anyone who cooks the designated Pesach lamb in water or any other liquid has violated the Torah's command.