Charles Ellicott Commentary 1 Chronicles 1:48

"And Samlah died, and Shaul of Rehoboth by the River reigned in his stead." — 1 Chronicles 1:48 (ASV)

Shaul. — Saul, the name of the first king of Israel.

Rehoboth by the river. — Probably the same as Rehoboth Ir in Genesis 10:11, i.e., the suburbs of Nineveh. The river is Euphrates.