To Abishai - Probably, as the king was on bad terms with Joab, and wished to deprive him of his post as Captain of the host, he gave his orders to Abishai, and weakly connived at the execution of them by Joab, which was inevitable.
Related Commentaries of 2 Samuel 20:6
2 Samuel 20:6
6 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 escapec us.