Mu'awiyah bin Qurrah bin Riyab, the grandson of Sayyiduna Riyab al-Muzani (may Allah be pleased with him), narrated from his father that he was with his grandfather (Riyab, may Allah be pleased with him) when, as a boy, he came to the Messenger of Allah (peace and blessings be upon him), and he found him (peace and blessings be upon him) with the buttons (of his collar) undone.
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4618