1 Chronicles 19:11
And the rest of the people he delivered unto the hand of Abishai his brother, and they set themselves in array against the children of Ammon. And the rest of the people he delivered unto the hand of Abishai his brother, and they set themselves in array against the children of Ammon.
Joab divided his forces to meet enemies on two fronts. He himself took command of one division to face the Syrians. The rest of the troops he placed under the command of his brother Abishai. That division under Abishai set itself in battle array against the Ammonites.