In the month of Abib, the month in which you left Egypt, celebrate the Festival of Unleavened Bread in the way that I commanded you. Do not eat any bread made with yeast during the seven days of this festival. Never come to worship me without bringing an offering. 1
References for Exodus 23:15
23.15 Ex 12.14-20; Lv 23.6-8; Nu 28.17-25.