1 Kings 1:51

And it was told Solomon
By some of his courtiers:

saying, behold, Adonijah feareth King Solomon;
lest he should take away his life:

for, lo, he hath caught hold on the horns of the altar;
which was the last resort of the guilty when they despaired of mercy otherwise:

saying, let King Solomon swear unto me this day that he will not slay
his servant with the sword;
he owns Solomon to be king, and himself his subject and servant; this no doubt he did to conciliate his favour, nor did he think his life safe, unless Solomon promised with an oath, that he would not take it away.