Exodus 15:22-25

22Then Moses led Israel from the Red Sea, and they went into the Wilderness of Shur; they went [a distance of] three days (about thirty-three miles) in the wilderness and found no water.

23Then they came to Marah, but they could not drink its waters because they were bitter; therefore it was named Marah (bitter).

24The people [grew discontented and] grumbled at Moses, saying, “What are we going to drink?”

25Then he cried to the Lord [for help], and the Lord showed him a tree, [a branch of] which he threw into the waters, and the waters became sweet. There the Lord made a statute and an ordinance for them, and there He tested them,