Exodus 34:18-35

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. All that first opens the womb is mine, all your male livestock, the firstborn of cow and sheep. The firstborn of a donkey you shall redeem with a lamb, or if you will not redeem it you shall break its neck. All the firstborn of your sons you shall redeem. No one shall appear before me empty-handed. Six days you shall work, but on the seventh day you shall rest; even in plowing time and in harvest time you shall rest. You shall observe the festival of weeks, the first fruits of wheat harvest, and the festival of ingathering at the turn of the year. Three times in the year all your males shall appear before the LORD God, the God of Israel. For I will cast out nations before you, and enlarge your borders; no one shall covet your land when you go up to appear before the LORD your God three times in the year. You shall not offer the blood of my sacrifice with leaven, and the sacrifice of the festival of the passover shall not be left until the morning.