will appoint against you someone who will lay bare your faults and hunt for your weaknesses, whether you are alive or dead. The Prophet (peace and blessings be upon him) said: “Whoever pursues his brother’s hidden flaws, Allah will pursue his flaws; and if Allah pursues a person’s flaws, He will disgrace him even inside his mother’s house.”
Yet if mentioning another’s shortcomings is done for the purpose of sincere counsel and clarification, there is no harm in it. Imagine someone wishes to enter into a transaction with a certain individual and comes to you for advice: “What do you think—should I deal with so-and-so?” Knowing that this person is unreliable in his dealings, you are duty-bound to disclose his fault as an act of advice. The evidence is the incident in which Fāṭimah bint Qays (Allah be pleased with her) was courted by three Companions: Usāmah ibn Zayd, Muʿāwiyah ibn Abī Sufyān, and Abū Jahm. She sought the Prophet’s counsel, saying, “So-and-so, so-and-so, and so-and-so have proposed to me.” He replied, “As for Abū Jahm, he beats women; and Muʿāwiyah is poor and has no wealth. Marry Usāmah.” He thus spoke of the two men in a way they would dislike, but solely as advice, not to broadcast their faults or disgrace them—there is a clear difference.
Similarly, if someone consults you, asking, “Should I study under so-and-so?” and you know that the person follows a deviant path, there is no blame in telling him, “Do not study with him.” Whether the deviation lies in creed, ideas, or methodology, and you fear its impact on the one seeking counsel, you are obliged to clarify the matter: “Do not seek knowledge from that individual; he has such-and-such issues.”