“Once when the king of Aram was at war with Israel, he took counsel with his officers. He said. ‘At such and such a place shall be my camp.’ But the man of God sent word to the king of Israel. ‘Take care not to pass this place, because the Arameans are going down there.’ The king of Israel sent word to the place of which the man of God spoke. More than once or twice he warned such a place so that it was on alert.”
Elisha, the man of God, was able to know the plans of the king of Aram, probably King Ben-hadad II. Elisha then sent word to the king of Israel, also unnamed but probably King Jehoram. He told the king of Israel, where the king of the Arameans was sending his troops. The king of Israel would then warn that place to be on alert for the Arameans. This happened more than once or twice. I am not sure why more prophets did not help the king this way.