On hearing this, David sent Joab1 out with the entire army of fighting men.
References for 2 Samuel 10:7
The Ammonites came out and drew up in battle formation at the entrance to their city gate, while the Arameans of Zobah and Rehob and the men of Tob and Maacah were by themselves in the open country.
Joab saw that there were battle lines in front of him and behind him; so he selected some of the best troops in Israel and deployed them against the Arameans.
He put the rest of the men under the command of Abishai2 his brother and deployed them against the Ammonites.
References for 2 Samuel 10:10