It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "By the One in whose Hand is my soul, you must certainly enjoin what is right, forbid what is wrong, seize the hand of the wrongdoer and firmly bend him back to the truth, or else Allah will strike your hearts against one another too, and will curse you just as He cursed them."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10229