Albert Barnes Commentary 1 Kings 2:9

"Now therefore hold him not guiltless, for thou art a wise man; and thou wilt know what thou oughtest to do unto him, and thou shalt bring his hoar head down to Sheol with blood." — 1 Kings 2:9 (ASV)

Hold him not guiltless - that is, “Do not treat him as an innocent man. Punish him as you in your wisdom deem best. Not capitally at once, but in such a way that he will likely, in the course of time, give you a just occasion to slay him.” So, at least, Solomon seems to have understood the charge. (See 1 Kings 2:36–46.)