1 Kings 2:9
Now therefore hold him not guiltless: for thou art a wise man, and knowest what thou oughtest to do unto him; but his hoar head bring thou down to the grave with blood. Now therefore hold him not guiltless: for thou art a wise man, and knowest what thou oughtest to do unto him; but his hoar head bring thou down to the grave with blood.
The instruction belongs to David's counsel to Solomon about men who were unworthy of confidence. With regard to Joab, it directed Solomon to act wisely, not to hold him guiltless but to hold him accountable for his bloodshed. With regard to Shimei, it warned that he was a dangerous and violent man who might stir rebellion or take Solomon's life if he had the opportunity.
In dealing with such men Solomon was to use the wisdom God had given him, refusing to treat disaffection, scheming, or deception as virtues. He was to firmly disapprove unfaithfulness in both business matters and spiritual matters. He was to choose only counselors whom he could fully trust, especially for sacred work.