Hadithcore
Mishkat al-Masabih, 4333

Abu Kabsha said the headgear worn by God's messenger's Companions was flat. (It is not clear whether the reference here is to headgear which was low and wide, or to wide sleeves. The former seems to be preferred. Cf. Mirqat, iv, 424.) Tirmidhi transmitted it, saying this is a tradition which is rejected.

وَعَن أبي كبشةَ قَالَ: كَانَ كِمَامُ أَصْحَابِ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بُطْحًا. رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حديثٌ مُنكر

References1 variant
In-Book Reference
Book 22, Hadith 26