1 Kings 1:52
And Solomon said, If he will shew himself a worthy man, there shall not an hair of him fall to the earth: but if wickedness shall be found in him, he shall die. And Solomon said, If he will shew himself a worthy man, there shall not an hair of him fall to the earth: but if wickedness shall be found in him, he shall die.
Solomon spared Adonijah for the time being rather than putting him to death at once. His continued safety was made expressly conditional on his conduct, requiring him to show himself a worthy man. The terms were that if wickedness or wrongdoing should be found in him, he would die. After David's death Adonijah was accordingly executed for his rebellion.