So Joab and Abishai his brother slew Abner,.... For though it was only Joab that gave him the thrust of which he died, Abishai was in the secret, and was consenting and advising to his death, and so an accessory to it; and might be present, ready to assist in it, if occasion required; and so Josephus expressly says, that Abishai his brother was with him when he drew his sword, and smote him:because he had slain their brother Asahel at Gibeon in the battle: which was no just reason at all; his blood was shed in war, this in peace, in cold blood, and under the guise of friendship; that was shed with reluctance, and after fair warning, and in defence of himself; but this wilfully in Joab, unawares to Abner, and in great deceit and hypocrisy; see 1Ki 2:5.
Ut supra. (Antiqu. l. 7. c. 1. sect. 6.