Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[132] After these, there met him a good and a righteous man, whose name was Jehonadab, and who had been his friend of old. He saluted Jehu, and began to commend him, because he had done every thing according to the will of God, in extirpating the house of Ahab. So Jehu desired him to come up into his chariot, and make his entry with him into Samaria; and told him that he would not spare one wicked man, but would punish the false prophets, and false priests, and those that deceived the multitude, and persuaded them to leave the worship of God Almighty, and to worship foreign gods; and that it was a most excellent and most pleasing sight to a good and a righteous man to see the wicked punished. So Jehonadab was persuaded by these arguments, and came up into Jehu's chariot, and came to Samaria. And Jehu sought out for all Ahab's kindred, and slew them. And being desirous that none of the false prophets, nor the priests of Ahab's god, might escape punishment, he caught them deceitfully by this wile; for he gathered all the people together, and said that he would worship twice as many gods as Ahab worshipped, and desired that his priests, and prophets, and servants might be present, because he would offer costly and great sacrifices to Ahab's god; and that if any of his priests were wanting, they should be punished with death. Now Ahab's god was called Baal; and when he had appointed a day on which he would offer those sacrifices, he sent messengers through all the country of the Israelites, that they might bring the priests of Baal to him. So Jehu commanded to give all the priests vestments; and when they had received them, he went into the house [of Baal], with his friend Jehonadab, and gave orders to make search whether there were not any foreigner or stranger among them, for he would have no one of a different religion to mix among their sacred offices. And when they said that there was no stranger there, and they were beginning their sacrifices, he set fourscore men without, they being such of his soldiers as he knew to be most faithful to him, and bid them slay the prophets, and now vindicate the laws of their country, which had been a long time in disesteem. He also threatened, that if any one of them escaped, their own lives should go for them. So they slew them all with the sword, and burnt the house of Baal, and by that means purged Samaria of foreign customs [idolatrous worship]. Now this Baal was the god of the Tyrians; and Ahab, in order to gratify his father-in-law, Ethbaal, who was the king of Tyre and Sidon, built a temple for him in Samaria, and appointed him prophets, and worshipped him with all sorts of worship, although, when this god was demolished, Jehu permitted the Israelites to worship the golden heifers. However, because he had done thus, and taken care to punish the wicked, God foretold by his prophet that his .sons should reign over Israel for four generations. And in this condition was Jehu at this time.