Albert Barnes Commentary 1 Kings 1:50

"And Adonijah feared because of Solomon; and he arose, and went, and caught hold on the horns of the altar." — 1 Kings 1:50 (ASV)

For an explanation of the “horns” of the altar, see the note on Exodus 27:2. The altar to which Adonijah fled was likely the one in the “tabernacle” mentioned in 1 Kings 1:39.