Numbers 21:13-15

Amplified Bible

¹³From there they journeyed on and camped on the other side of [the river] Arnon, which is in the wilderness that extends from the boundary of the Amorites; for [the river] Arnon is the boundary of Moab, between Moab and the Amorites. ¹⁴That is why it is said in the ^[a]Book of the Wars of the Lord:

“^[b]Waheb in ^[c]Suphah,
And the ^[d]wadis of the Arnon [River],
¹⁵
And the slope of the wadis
That stretches toward the site of Ar
And leans to the border of Moab.”

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Footnotes

Numbers 21:14 A non-canonical work which, unfortunately, has been lost.
Numbers 21:14 Possibly a well that is the source of the Arnon river.
Numbers 21:14 Probably a place in Moab. However some of the rabbis took Suphah to be a reference to the Red Sea (Yam Suph in Hebrew) and maintained that these words imply God performed miracles for Israel in the valleys of Arnon such as He did at the Red Sea.
Numbers 21:14 Dry valleys of seasonal rivers.