Matthew Poole and continuators on Deuteronomy 16:3

3 Thou shalt eat no leavened bread with it , seven dayes shalt thou eat unleavened bread therewith, even the bread of affliction (for thou camest forth out of the land of Egypt in haste) that thou mayest remember the day when thou camest forth out of the land of Egypt, all the dayes of thy life.

To wit, with the Passeover, in the sense delivered: Or, in it, i. e. during the time of the feast of the Passeover.

(i. e.) Bread which is not usual nor pleasant, but unsavoury and unwholesome, to put thee in mind both of thy miseries endured in Egypt and of thy hasty coming out of it, which allowed thee no time to leaven or to prepare thy Bread.

Marginal references: Exod. 12. 15.