In a hadith Qudsi, Allah says “My slaves, I have forbidden injustice to myself and ahve forbidden it between you so do not wrong each other”.
Part of that which is forbidden is a Muslim’s humiliation of his brother. Because the Mu’min is ordered to help his brother. The Prophet s.a.w said “Help your
brother whether he is wrongdoing or wronged” He asked “Messenger of Allah, I will help him when he is wronged but how can I help him if he is wrongdoing” He (s.a.w) answered. “Prevent him from doing wrong, because that will be your helping him.” (Bukhari)
Abu Dawud narrated a hadith of Abu Talhah al-Ansari and Jabir ibn Abdullah that the Prophet s.a.w said. “Any Muslim man who humiliates a Muslim man in a place wherein his respect is violated and his honour reduced. Allah will humiliate him in a place wherein he would love His help. Any man who helps a Muslim in a place in which his honour is reduced and his respect violated then Allah will help him in a place in which he would love His help” (Abu Dawud)
Imam Ahmad narrated in a hadith of Umamah ibn Sahl from his father that the Prophet s.a.w said. “If in someone’s presence a Mu’min is humiliated and he doesn’t help him even though he is able to help him, Allah will humiliate him in front of all people on the Day of Rising.” (Ahmad)
Al-Bazzar narrated a hadith of Imran ibn Husayn that the Prophet s.a.w said. “Whoever helps his brother in his absence while he is able to help him, Allah will help him in the dunya and the akhirah.’ (AL-Bazzar)
(from “The Compendium of Knowledge and Wisdom” by Ibn Rajab al-Hanbali)