And from Ibn Umar, may Allah be pleased with them both, he said: I heard the Prophet, peace and blessings be upon him, say: "Whoever says to his brother, 'O disbeliever,' then it returns to one of them. If he was as he said, then it returns to him." Narrated by Muslim.

Therefore, takfir (declaring someone an infidel) is one of the legal rulings that refer back to the Book and the Sunnah. It is obligatory to be extremely cautious in this matter. No one should be declared an infidel or a fasiq (a transgressor) except for whom the Book and the Sunnah indicate his disbelief or transgression. The general principle for a Muslim who appears to be just is the continuation of his Islam and the continuation of his justice until it is confirmed that these have been removed from him by virtue of legal evidence.

And among the greatest issues that have been a cause for declaring many Muslims as infidels without legal evidence is the absolute application of the rule: "Whoever does not declare the disbeliever an infidel is an infidel," without legal controls to govern and clarify it. This issue is one of the great matters in which feet have stumbled, understandings have gone astray, and pens have been reckless. So many Muslims have become unhesitating in declaring as an infidel one who refrains from declaring as an infidel the one who commits disbelief and attributes himself to Islam (out of ignorance or misinterpretation)...!! For whoever affirms Islam for the one who commits disbelief, he affirms Islam for him based on what he has shown of the rituals of Islam, not based on what he has done of disbelief. In reality, he is refraining from declaring him an infidel out of fear of falling into what is forbidden, not out of his ignorance of faith and monotheism, or in rejection of the legal ruling. For takfir is a legal ruling, and when a Muslim utters the two testimonies, he has fulfilled the basis of religion. A common Muslim man may be declared an infidel by the Taghut (idol or false deity) by disavowing man-made laws, for example, and avoiding them, disliking them, and denying them. However, he may be ignorant of the ruling concerning this ruler who utters the two testimonies, prays, and fasts, and the like. So he fears falling into declaring a Muslim an infidel because he does not know the conditions, pillars, and impediments of apostasy.