Q 1: Is it allowed to reprove a Muslim because he believes that pictures are permissible? What things are permissible to denounce? The Prophet (peace be upon him) said, "Whoever among you sees something abominable should rectify it with his hand..." Allah (Exalted be He) said: You [true believers in Islâmic Monotheism, and real followers of Prophet Muhammad صلى الله عليه وسلم) and his Sunnah] are the best of peoples ever raised up for mankind; you enjoin Al-Ma‘rûf (i.e. Islâmic Monotheism and all that Islâm has ordained) and forbid Al-Munkar (polytheism, disbelief and all that Islâm has forbidden)

(Part No. 12; Page No. 346)  A: The Islamic Shari`ah (Islamic law) includes all that Allah (Exalted be He) ordained such as the five prayers, fasting Ramadan, and other acts of worship enjoined by Him, as it includes what He prohibited, such as illicit sexual intercourse, theft, killing a person without legal excuse, and other matters which Allah (Exalted be He) and His Messenger prohibited. Therefore, whoever fell short in observing what Allah forbade, should be advised by anyone who is able to denounce such evil in the way which the Messenger of Allah explained in his saying: "Whoever, among you, sees something abominable should rectify it with his hand; and if he has not strength enough to do it, then he should do it with his tongue; and if he has not strength enough to do it, (even) then he should (abhor it) from his heart, and that is the least of Faith." According to another Hadith: Beyond that there is no faith even to the extent of a mustard seed. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.