Musannaf Ibn Abi Shayba 16:571

Abu Bakr narrated to us, he said: al-Fadl ibn Dukayn narrated to us, from Zuhayr, from Urwah ibn Abdullah ibn Qushayr, he said: Muawiyah ibn Qurrah narrated to me, from his father, he said: I came to the Messenger of Allah, may Allah bless him and grant him peace, and I pledged allegiance to him, and his shirt was unbuttoned. Urwah said: I never saw Muawiyah nor his son, in winter or summer, except that their buttons were unfastened.