Absalom set AMASA over the army instead of Joab. Now AMASA was the son of a man whose name was Ithra the Israelite, who went in to Abigail the daughter of Nahash, sister to Zeruiah, Joab's mother.
1 Chronicles 2:17
Abigail bore AMASA; and the father of AMASA was Jether the Ishmaelite.