1 Kings 2:4-5

4so that the Lord may fulfill His promise concerning me, saying, ‘If your sons are careful regarding their way [of life], to walk before Me in truth with all their heart and mind and with all their soul, you shall not fail to have a man (descendant) on the throne of Israel.’

5Now you also know what Joab the son of Zeruiah [my sister] did to me, and what he did to the two commanders of the armies of Israel, to Abner the son of Ner and to Amasa the son of Jether, [both of] whom he murdered; avenging the blood of war in [a time of] peace. And he put the [innocent] blood of war [of Abner and Amasa] on his belt that was around his waist, and on his sandals on his feet.