Exodus 15:23

And when they came to Marah, the water was no good for drinking, for the waters of Marah were bitter, which is why it was named Marah.

Numbers 33:8

And journeying on from before Hahiroth, they went through the sea into the waste land: they went three days' journey through the waste land of Etham and put up their tents in Marah.

Ruth 1:20

And she said to them, Do not let my name be Naomi, but Mara, for the Ruler of all has given me a bitter fate.

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
And journeying on from before Hahiroth, they went through the sea into the waste land: they went three days' journey through the waste land of Etham and put up their tents in Marah.
Ruth 1:20
And she said to them, Do not let my name be Naomi, but Mara, for the Ruler of all has given me a bitter fate.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain