Cross reference
Exodus 15:23
23 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.
Numbers 33:8
8 And they journeyed from before Hahiroth, and passed through the midst of the sea into the wilderness: and they went three days' journey in the wilderness of Etham, and encamped in Marah.
Ruth 1:20
20 And she said unto them, Call me not Naomi, call me Mara; for the Almighty hath dealt very bitterly with me.