Exodus 3:12

3:12 He replied, “Surely I will be with you, and this will be the sign to you that I have sent you: When you bring the people out of Egypt, you and they will serve God on this mountain.”

Exodus 3:18

3:18 “The elders will listen to you, and then you and the elders of Israel must go to the king of Egypt and tell him, ‘The Lord, the God of the Hebrews, has met with us. So now, let us go three days’ journey into the wilderness, so that we may sacrifice to the Lord our God.’