Commentary for I Kings 1:50

Of the horns [of the corners] of the Altar. Which was in Givon.³⁶Alternatively, he grabbed on to the corners of the altar that was in Yerushalayim.—Radak. In those days it was permissible to build an altar and bring certain sacrifices outside of the Mishkan. He said, “Those who are executed by Beis Din are buried in the graves of Beis Din. I will die here, and be buried in the graves of my forefathers.” Thus did Rabbi Tanchuma expound.

and caught hold of the horns of the altar: It was already explained in Torah that the altar shelters only if a murderer who killed with malice and cunning comes there. Thus Adonijah came there because there he would not fear that Solomon would kill him, and the place would be a shelter for him until Solomon the king should promise not to put him to death.