Exodus 12:14-16, 37-39

“This will be a memorial day for you; you will celebrate it as a festival to GOD down through the generations, a fixed festival celebration to be observed always. You will eat unraised bread (matzoth) for seven days: On the first day get rid of all yeast from your houses—anyone who eats anything with yeast from the first day to the seventh day will be cut off from Israel. The first and the seventh days are set aside as holy; do no work on those days. Only what you have to do for meals; each person can do that.

The Israelites moved on from Rameses to Succoth, about 600,000 on foot, besides their dependents. Hebrews and non-Hebrews alike set out, not to mention the large flocks and herds of livestock. They baked unraised cakes with the bread dough they had brought out of Egypt; it hadn’t raised—they’d been rushed out of Egypt and hadn’t time to fix food for the journey.