Exodus 12:8, 18, 34, 39

Then they shall eat the flesh on that night; roasted in fire, with unleavened bread and with bitter herbs they shall eat it.

In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, until the twenty-first day of the month at evening.

So the people took their dough before it was leavened, having their kneading bowls bound up in their clothes on their shoulders.

And they baked unleavened cakes of the dough which they had brought out of Egypt; for it was not leavened, because they were driven out of Egypt and could not wait, nor had they prepared provisions for themselves.