Exodus 15:22-16:1 (Vespers - Exaltation of the Cross)
Moses led Israel onward from the Red Sea, and they went into the wilderness of Shur; they went three days in the wilderness and found no water. When they came to Marah, they could not drink the water of Marah because it was bitter; therefore it was named Marah. And the people murmured against Moses, saying, "What shall we drink?" And he cried to the LORD; and the LORD showed him a tree, and he threw it into the water, and the water became sweet. There the LORD made for them a statute and an ordinance and there he proved them, saying, "If you will diligently hearken to the voice of the LORD your God, and do that which is right in his eyes, and give heed to his commandments and keep all his statutes, I will put none of the diseases upon you which I put upon the Egyptians; for I am the LORD, your healer."
Then they came to Elim, where there were twelve springs of water and seventy palm trees; and they encamped there by the water. They set out from Elim, and all the congregation of the people of Israel came to the wilderness of Sin, which is between Elim and Sinai, on the fifteenth day of the second month after they had departed from the land of Egypt.