A Muslim is the brother of a Muslim
الْمُسْلِمُ أَخُو الْمُسْلِمِ، لَا يَظْلِمُهُ وَلَا يَخْذُلُهُ وَلَا يَحْقِرُهُ
Al-muslimu akhu-l-muslim, la yazlimuhu wa la yakhdhuluhu wa la yahqiruh.
"A Muslim is the brother of a Muslim, he does not wrong him, abandon him, or look down on him."
Narrated by Abu Hurayrah. Sahih Muslim 2564 · Nawawi's Forty · #35
A short reflection
A Muslim has obligations of posture before obligations of deeds. You don't oppress, you don't abandon, you don't despise. Everything else flows from there.