Adam Clarke on 1 Kings 19:17

Shall Elisha slay - We do not find that Elisha either used the sword, or commissioned it to be used, though he delivered solemn prophecies against this disobedient people: and this is probably the sense in which this should be understood, as Elisha was prophet before Hazael was king, and Hazael was king before Jehu; and the heavy famine which he brought on the land took place before the reign either of Jehu or Hazael. The meaning of the prophecy may be this: Hazael, Jehu, and Elisha, shall be the ministers of my vengeance against this disobedient and rebellious people. The order of time, here, is not to be regarded.