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

[197] Among them came Ahithophel the Gilonite, a counsellor of David's, and two hundred men out of Jerusalem itself, who knew not his intentions, but were sent for as to a sacrifice. So he was appointed king by all of them, which he obtained by this stratagem. As soon as this news was brought to David, and he was informed of what he did not expect from his son, he was aftrighted at this his impious and bold undertaking, and wondered that he was so far from remembering how his offense had been so lately forgiven him, that he undertook much worse and more wicked enterprises; first, to deprive him of that kingdom which was given him of God; and secondly, to take away his own father's life. He therefore resolved to fly to the parts beyond Jordan: so he called his most intimate friends together, and communicated to them all that he had heard of his son's madness. He committed himself to God, to judge between them about all their actions; and left the care of his royal palace to his ten concubines, and went away from Jerusalem, being willingly accompanied by the rest of the multitude, who went hastily away with him, and particularly by those six hundred armed men, who had been with him from his first flight in the days of Saul. But he persuaded Abiathar and Zadok, the high priests, who had determined to go away with him, as also all the Levites, who were with the ark, to stay behind, as hoping that God would deliver him without its removal; but he charged them to let him know privately how all things went on; and he had their sons, Ahimmaz the son of Zadok, and Jonathan the son of Abiathar, for faithful ministers in all things; but Ittai the Gitrite went out with him whether David would let him or not, for he would .have persuaded him to stay, and on that account he appeared the more friendly to him. But as he was ascending the Mount of Olives barefooted, and all his company were in tears, it was told him that Ahithophel was with Absalom, and was of his side. This hearing augmented his grief; and he besought God earnestly to alienate the mind of Absalom from Ahithophel, for he was afraid that he should persuade him to follow his pernicious counsel, for he was a prudent man, and very sharp in seeing what was advantageous. When David was gotten upon the top of the mountain, he took a view of the city; and prayed to God with abundance of tears, as having already lost his kingdom; and here it was that a faithful friend of his, whose name was Hushai, met him. When David saw him with his clothes rent, and having ashes all over his head, and in lamentation for the great change of affairs, he comforted him, and exhorted him to leave off grieving; nay, at length he besought him to go back to Absalom, and appear as one of his party, and to fish out the secretest counsels of his mind, and to contradict the counsels of Ahithophel, for that he could not do him so much good by being with him as he might by being with Absalom. So he was prevailed on by David, and left him, and came to Jerusalem, whither Absalom himself came also a little while afterward.