And David said to Abishai, “Now Sheba the son of Bichri will do us more harm than Absalom. Take your lord’s servants and pursue him, lest he get himself to fortified cities and escape from us.”
We have here Amasa's fall just as he began to rise. He was nephew to David (Sa2 17:25), had been Absalom's general and commander-in-chief of his rebellious army, but, that being routed, he came over into David's interest, upon a promise that he should be general of his forces instead of Joab.
Commenting on 2 Samuel 20:4-13
And David said to Abishai,.... For it seems he would have nothing to say to Joab, being displeased with him for slaying Absalom, and having removed him from his posts; and therefore speaks to the next officer in his army, Abishai; though Josephus (p) says, he addressed himself to Joab, contrary to the express words of the text: now shall Sheba the son of Bichri...
And David said to Abishai, Now shall Sheba the son of Bichri do us more harm than [did] Absalom: take thou thy lord's servants, and pursue after him, lest he get him fenced cities, and escape us. (f) Either those who had been under Joab or David's men.