The Reward of Enjoining Good and Forbidding Evil
Sayyidatina 'Aisha, (may Allah be pleased with her) said: "Once the Holy Prophet Muhammad, (may Allah's blessings and peace be upon him), entered the house, and I guessed from his face that something had happened to him. He did not talk to
anyone, and after having ablution he entered the mosque. I tried to hear behind the wall what he said. So, he sat at the pulpit, and after praising Allah (The Glorified and the Exalted) he said: 'O Muslims! Allah has commanded you to exhort people to good deeds and prevent them from sins; otherwise a time will come when you will pray to Him, but He will not listen to you; you will ask your needs of Him, but He will not grant them; you will demand His help against your enemies, but He will not help you.' After saying this, he came down from the pulpit". (Ibn Majah)
The Reward of Enjoining Good and Punishment for Enjoining Evil
Hadrat Abu Huraira (may Allah be pleased with him) reported Prophet Muhammad (may Allah's blessings and peace be upon him) as saying, "If anyone summons others to follow right guidance, his reward will be equivalent to those of the people who follow him without their rewards being diminished in any respect on that account; and if anyone summons others to follow error, the sin of which he is guilty will be equivalent to those of the people who follow him without their sins being diminished in any respect on that account." (Muslim)
Right Guidance is clear from Error
Hadrat Ibn 'Abbas (may Allah be pleased with him) reported Prophet Muhammad (may Allah's blessings and peace be upon him) as saying, "Things are of three categories: a matter whose right guidance is clear, which you must follow; a matter whose error is clear, which you must avoid; and a matter about which there is a difference of opinion, which you must entrust to Allah." (Ahmad)
Truth is clear from Falsehood
Hadrat Imam Al-Hasan bin 'Ali (may Allah be pleased with him) said: "I have retained in my memory these words of Allah's Messenger (may Allah's blessings and peace be upon him), 'Leave what causes you doubt and turn to what does not cause you doubt. Truth is tranquility, but falsehood is doubt.' " (Ahmad, Tirmidhi and Nasai)
Practice what you preach
Hadrat Usama bin Zaid (may Allah be pleased with him) reported Prophet Muhammad (may Allah's blessings and peace be upon him) as saying, "A man will be brought on the Day of Resurrection and cast into hell, and his intestines will pour forth in hell and he will go round in them as an ass goes round with its millstone. The inhabitants of hell will gather round him and say, 'What has happened to you, so and so? Were you not enjoining us to do what was reputable and forbidding us to do what was disreputable?' He will reply, 'I was enjoining you to do what was reputable, but was not doing it myself; and I was forbidding you to do what was disreputable, but was doing it myself.' " (Bukhari and Muslim)