Hadith 5452
Muawiyah bin Qurrah narrates from his father: I, along with some people from the tribe of Muzaynah, presented myself before the Prophet Muhammad (peace be upon him). We pledged allegiance on his blessed hand. I saw that the collar of the Prophet (peace be upon him) was open, so I put my hand inside it and touched the Seal of Prophethood.
The narrator says: I saw Muawiyah bin Qurrah and his father always kept their collars open in every season, whether it was hot or cold. They never buttoned them.