What did God tell Moses to lift up over the sea so it would divide?

Answer: His staff

God said, "Lift up your staff and stretch out your hand over the sea and divide it," so Israel could cross on dry ground.

“And as for you, lift up your staff and stretch out your hand over the sea and divide it, so that the Israelites can go through the sea on dry ground.”— Exodus 14:16 (BSB)