1 Kings 22:4
And he said unto Jehoshaphat, Wilt thou go with me to battle to Ramoth-gilead? And Jehoshaphat said to the king of Israel, I am as thou art, my people as thy people, my horses as thy horses. And he said unto Jehoshaphat, Wilt thou go with me to battle to Ramoth-gilead? And Jehoshaphat said to the king of Israel, I am as thou art, my people as thy people, my horses as thy horses.
Jehoshaphat agreed to join Ahab, king of Israel, in battle at Ramoth-gilead against the Syrians, pledging that his people and horses would act together with Ahab's people and forces as one united force. Ahab's purpose in the campaign was to recover Ramoth-gilead, which he claimed rightfully belonged to Israel. Jehoshaphat's promise to unite their forces was a rash act made in a moment of weakness.
That pledge bound him to an alliance that was not in God's order. Even after Micaiah warned that the campaign would fail, Jehoshaphat was reluctant to withdraw from his pledge.