דברי הימים א, פרק ה׳, פסוק י׳

During the reign of King Saul, the tribe of Reuben launched a military campaign to expand their territory. Their target was the Hagrites, an Arab tribe. The primary approach among commentators is that these people were Ishmaelites, who took their name from their matriarch, Hagar [רד״ק]. The conflict resulted in a decisive victory, with the Hagrites suffering total defeat and falling into the hands of the Reubenites [ביאור שטיינזלץ].

Following the battle, the victorious Reubenites moved directly into the dwellings left behind by their enemies. They took over and settled in the very tents that had previously belonged to the Hagrites [מצודת דוד]. Living in tents was deeply characteristic of the local Arab lifestyle and customs during that era [רש״י]. The newly conquered domain was vast, stretching across the entire eastern front facing the region of Gilead [מצודת דוד, רד״ק]. Ultimately, this successful expansion during the days of Saul brought about a significant shift in the territorial boundaries and settlement map of the entire region [מלבי״ם].