C. F. Keil and Franz Delitzsch on 1 Chronicles 5:19

1Ch 5:19 “They made was with the Hagarites and Jethur, Nephish and Nodab.” So early as the time of Saul the Reubenites had victoriously made war upon the Hagarites (see 1Ch 5:10); but the war here mentioned was certainly at a later time, and has no further connection with that in 1Ch 5:10 except that both arose from similar causes. The time of the second is not given, and all we know from 1Ch 5:22 is that it had broken out before the trans-Jordanic Israelites were led captive by the Assyrians. הגריאים, in Psa 83:7 contracted into הגרים, are the Ἀγραῖοι, whom Strabo, xvi. p. 767, introduces, on the authority of Eratosthenes, as leading a nomadic life in the great Arabico-Syrian desert, along with the Nabataeans and Chaulotaeans. Jetur, from whom the Itureans are descended, and Nephish, are Ishmaelites; cf. on Gen 25:15. Nodab, mentioned only here, is a Bedouin tribe of whom nothing more is known.