ציטירנדיקער פּירוש אויף דברי הימים א 18:12

and Joab returned and smote of Edom, etc. [of] the eighteen thousand stated in Scripture (II Sam. 8:13, I Chron. 18:12), Abishai slew six thousand the first time, and Joab slew twelve thousand when he returned from battling Aram.

When he fought Heb. בהצותו, as (Num. 26:9): “when they quarreled (בהצותם) with the Lord,” that he fought with them because they aided the Ammonites.