Exodus 34:17-19 New Revised Standard Version (NRSV)
17 You shall not make cast idols.
18 You shall keep the festival of unleavened bread. Seven days you shall eat unleavened bread, as I commanded you, at the time appointed in the month of Abib; for in the month of Abib you came out from Egypt.
19 All that first opens the womb is mine, all your male[a] livestock, the firstborn of cow and sheep.