Adam Clarke on 1 Samuel 30:9

The brook Besor - This had its source in the mountain of Idumea, and fell into the Mediterranean Sea beyond Gaza. Some suppose it to have been the same with the river of the wilderness, or the river of Egypt. The sense of this and the following verse is, that when they came to the brook Besor, there were found two hundred out of his six hundred men so spent with fatigue that they could proceed no farther. The baggage or stuff was left there, 1Sam 30:24, and they were appointed to guard it.