Musnad Ahmad 25:40

Marwan ibn Shuja' narrated to us, Khasif narrated to me, from Mujahid, from Ibn Abbas, that he performed Tawaf of the House with Mu'awiyah. Mu'awiyah began to touch all the corners [of the Kaaba]. Ibn Abbas said to him, "Why do you touch these two corners, when the Messenger of Allah (peace and blessings of Allah be upon him) did not touch them?" Mu'awiyah said, "Nothing of the House is to be abandoned." Ibn Abbas said, "There has certainly been for you in the Messenger of Allah an excellent pattern [Al-Ahzab: 21]." Mu'awiyah said, "You have spoken the truth."