It is narrated from Sayyiduna Sahl bin Hunayf (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever has a believer humiliated in his presence and does not help him, while he is able to help him, Allah will humiliate him before all (the witnesses) on the Day of Resurrection."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5533