Awrah For Men In Front Of Other Men
In Farahi school, Quran and sunnah are the primary sources for Guidance and Hadith are considered as secondary source . Ghamidi sb understanding comes from Quranic verse Surah Nur 30-31. The minimum requirement that needs to be fulfilled in all circumstances and falls under the directive of ‘ وَيَحْفَظُوا فُرُوجَهُمْ ‘.. Based on Ghamidi sb understanding, covering from belly to knee is essential satr for men. Hence, NO NEED OF HADITH REFERENCE!
Being in shirt is commendable but it is not a sin if you remove it. In my previous response, by belly i meant navel.