The fighting lasted all day, with Ahab propped up in his chariot so he could see the Syrian troops. He bled so much that the bottom of the chariot was covered with blood, and by evening he was dead.
You will know, because if the LORD says something will happen, it will happen. And if it doesn't, you will know that the prophet was falsely claiming to speak for the LORD. Don't be afraid of any prophet whose message doesn't come from the LORD.