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.

حَدَّثَنَا النُّفَيْلِيُّ، وَأَحْمَدُ بْنُ يُونُسَ، قَالاَ حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا عُرْوَةُ بْنُ عَبْدِ اللَّهِ، - قَالَ ابْنُ نُفَيْلٍ ابْنُ قُشَيْرٍ أَبُو مَهَلٍ الْجُعْفِيُّ - حَدَّثَنَا مُعَاوِيَةُ بْنُ قُرَّةَ، حَدَّثَنِي أَبِي قَالَ، أَتَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فِي رَهْطٍ مِنْ مُزَيْنَةَ فَبَايَعْنَاهُ وَإِنَّ قَمِيصَهُ لَمُطْلَقُ الأَزْرَارِ - قَالَ - فَبَايَعْتُهُ ثُمَّ أَدْخَلْتُ يَدِي فِي جَيْبِ قَمِيصِهِ فَمَسِسْتُ الْخَاتَمَ ‏.‏ قَالَ عُرْوَةُ فَمَا رَأَيْتُ مُعَاوِيَةَ وَلاَ ابْنَهُ قَطُّ إِلاَّ مُطْلِقِي أَزْرَارِهِمَا فِي شِتَاءٍ وَلاَ حَرٍّ وَلاَ يُزَرِّرَانِ أَزْرَارَهُمَا أَبَدًا ‏.‏