Musnad Ahmad 25:372

Hassan ibn Musa narrated to us, Abu Khaythama narrated to us, from Abdullah ibn Uthman ibn Khuthaym, from Abu al-Tufayl, who said: I saw Muawiyah performing Tawaf of the House, and Abdullah ibn Abbas was to his left, and I was following them, behind their backs, hearing their speech. Muawiyah began to touch the corner of the Black Stone. Abdullah ibn Abbas said to him: "Indeed, the Messenger of Allah, may Allah bless him and grant him peace, did not touch these two corners." Muawiyah said: "Leave me be, O Ibn Abbas, for there is nothing of it that is abandoned." Ibn Abbas continued, not adding anything more to him; every time he placed his hand on any part of the two corners, he would say that to him.