Exodus 15:23

and they come in to Marah, and have not been able to drink the waters of Marah, for they are bitter; therefore hath one called its name Marah.

Numbers 33:8

And they journey from Pi-Hahiroth, and pass over through the midst of the sea, into the wilderness, and go a journey of three days in the wilderness of Etham, and encamp in Marah.

Ruth 1:20

And she saith unto them, 'Call me not Naomi; call me Mara, for the Almighty hath dealt very bitterly to me,

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 they journey from Pi-Hahiroth, and pass over through the midst of the sea, into the wilderness, and go a journey of three days in the wilderness of Etham, and encamp in Marah.
Ruth 1:20
And she saith unto them, 'Call me not Naomi; call me Mara, for the Almighty hath dealt very bitterly to me,