Exodus 15:23

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

Numbers 33:8

They moved out from before Pi-hahiroth and passed through the midst of the [Red] Sea into the wilderness; and they went a three days’ journey in the Wilderness of Etham and camped at Marah.

Ruth 1:20

She said to them, “Do not call me Naomi (sweetness); call me Mara (bitter), for the Almighty has caused me great grief and bitterness.

Treasury of Scripture Knowledge

Summary

And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah.

Bible References

Marah

Numbers 33:8
They moved out from before Pi-hahiroth and passed through the midst of the [Red] Sea into the wilderness; and they went a three days’ journey in the Wilderness of Etham and camped at Marah.
Ruth 1:20
She said to them, “Do not call me Naomi (sweetness); call me Mara (bitter), for the Almighty has caused me great grief and bitterness.