1 Kings 13:3

And he gave a sign the same day The sign was necessary because the event foretold was to be at so remote a date that none who were living in Jeroboam's day would be alive to see it. Hence to assure them that it would come to pass a startling token of the power in which the prophet spake is exhibited by the rending of the altar and the scattering of what was on it in the presence of all who stood by. The word מופת rendered -sign", is much more frequently used of -wonders" and -miracles", and it has that sense in some degree here. With this we may compare the use of τέρας as well as σημεῖον for the miracles of the New Testament.

and the ashes thatare upon it The Hebrew word, which is the same as that so often rendered -fatness", applies only to the ashes of an altar, which would be mixed up with the fat of sacrifices burnt upon it. Hence the LXX. renders by ἡ πιότης -the fat", or -fatness".