1 Kings 1:51

And it was told Solomon, saying, Behold, Adonijah feareth king Solomon: for, lo, he hath caught hold on the horns of the altar, saying, Let king Solomon swear unto me to day that he will not slay his servant with the sword.

Cross-reference

Exodus 21:14 Historical context

Exodus 21:14 limits sanctuary for willful murder — the legal basis for Solomon's conditional sparing of Adonijah.