Lewis & Short

Ismaël, ēlis, or indecl., m., Abraham’s son by Hagar, Ishmael, Vulg. Gen. 16, 15 sqq.; gen. Ismaël, id. ib. 25, 12: -ēlis, id. ib. 25, 16.
Hence, Ismăēlītes, ae, m., a descendant of Ishmael, Vulg. 1 Par. 2, 17; id. Gen. 37, 27.