Qurra bin Iyas reported,

I came to the Messenger of Allah ﷺ with a group from Mazina, and we pledged allegiance to him while the buttons of his shirt were undone. So I pledged allegiance to him, then I slipped my hand into the opening of his shirt and touched the Seal of Prophethood.Urwa said, "I never saw Muawiya or his son but with their shirt buttons undone, in winter or summer alike. They never fastened their buttons at all."

Azami 15358

Sahih

عن معاوية بن قرة، حدثني أبي، قال

أتيت رسول الله ﷺ في رهط من مزينة، فبايعناه، وإن قميصه لمطلق الأزرار، قال: فبايعته ثم أدخلت يدي في جيب قميصه، فمسست الخاتم. قال عروة: فما رأيت معاوية ولا ابنه قط، إلا مطلقي أزرارهما في شتاء ولا حر، ولا يزرران أزرارهما أبدا.

الأعظمي 15358صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Clothing and adornment
Chapter
Types of clothing and its colors
Section
Unbuttoning
Numbering
Jami al-Kamil 15358 (2nd edition)
Azami 15358