How authentic is the narration that includes Muawiyah's statement: "Behold, everything I have granted Al-Hasan ibn Ali is beneath these two feet of mine, and I will not fulfill it," and Abu Ishaq's commentary: "And by Allah, he was treacherous"?

This narration was mentioned by Abu al-Faraj al-Isfahani in his book Maqatil al-Talibiyyin, and no one else mentioned it with this chain of transmission or any other. No scholar has judged it as authentic or weak. One must be cautious of what Abu Faraj al-Isfahani narrates, as Ibn Taymiyyah weakened him and accused him regarding his transmissions.