Mu'awiyah b. Qurrah quoted his father as saying:I came to the Messenger of Allah (ﷺ) with a company of Muzainah and we swore allegiance to him. The buttons of his shirt were open. I swore allegiance to him and I put my hand inside the collar of his shirt and felt the seal. 'Urwah said: I always saw Mu'awiyah and his son opening their buttons of the collar during winter and summer. They never closed their buttons

English translation · Sunan Abu Dawud