Exodus 12:37-39

37That night the people of Israel left Rameses and started for Succoth. There were about 600,000 men, plus all the women and children.

38A rabble of non-Israelites went with them, along with great flocks and herds of livestock.

39For bread they baked flat cakes from the dough without yeast they had brought from Egypt. It was made without yeast because the people were driven out of Egypt in such a hurry that they had no time to prepare the bread or other food.