And one told David, saying, Ahithophel is among the conspirators with Absalom. And David said, O LORD, I pray you, turn the counsel of Ahithophel into foolishness.
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Augustine of Hippo
Was it not by Absalom’s own will that he chose to follow advice that proved detrimental to him, though he only did so because the Lord had heard his father’s prayer to this effect? - "On Grace and Free Will 20.41"
Thus, then, the Lord knew how to bring to nothing the counsels of nations. We learned in the time of Ahithophel how he cast away the counsels of the princes, when David prayed, saying, “Infatuate the counsel of Ahithophel.” Therefore, when you hear someone making great threats and announcing that he will bring upon you all sorts of ill treatment, losses, blows or death, look up to the Lord who brings to nothing the counsels of nations and rejects the devices of the people. - "Homilies on the Psalms 32.6" ...