The Messenger of Allah ﷺ said, "Shabbiness is part of faith." He explained that shabbiness means austerity, that is, living simply.
حدثنا كثير بن عبيد الحمصي حدثنا أيوب بن سويد عن أسامة بن زيد
قال رسول الله ﷺ البذاذة من الإيمان قال البذاذة القشافة يعني التقشف
No references are available.
[Its chain is daif] Narrated by Abu Dawud in the Book of Combing the Hair, chapter on the prohibition of excessive luxury in grooming, vol/no. 4161, from the hadith of Abdullah bin Abu Umama, with similar wording. Tahawi also narrated it in Mushkil Athar, 4,478/1/151, and Tabarani narrated it, 1/272, through two routes from Abu Umama, with similar wording. Ibn Ishaq's transmission uses "an" (indicating a possible break in the chain).