An Obligation to Warn Others
Shaikh Rabīʿ ibn Hādī Al-Madkhalī, may Allāh protect him, said:
Al-Nawawī relates a consensus on this. And Ibn Rajab relates—and other than he from among the scholars [of Islam]—that it is an obligation to speak disparagingly and critically of someone who causes harm to Muslims in their religion or worldly affairs […] but not out of desire—only out of wanting good for Muslims.
Majmūʿ Al-Fatāwá li-l-Shaikh Rabīʿ ibn Hādī Al-Madkhalī, vol. 14, p. 254.