Q24. It's mentioned in the authentic Hadīth: "Whoever says to his brother O Kāfir, then surely one of them is such" so is this from the Nullifiers (of Islām)?
A. What appears to me, and Allāh (جل وعلا) knows best, is that the Takfīr of a Muslim is divided into three categories:
1. The one who had Ta'wīl in his speech (of calling the muslim a Kāfir), there's no sin upon him, rather he could be rewarded as it was affirmed by several Scholars (i.e. Such as ibn al-Qayyim).
And this is indicated by 'Umar's (رضي الله عنه) saying to Hātib (رضي الله عنه): "Allow me to strike the neck of this hypocrite".
And the saying of Usayd(رضي الله عنه) to Sa'd ibn 'Ubādah(رضي الله عنه): "Indeed you're a hypocrite, you argue on behalf of the hypocrites".
And other than that, and al-Bukhārī (رحمه الله) has written a chapter-heading based upon that in al-Adab al-Mufrad:
"The chapter of whoever doesn't view the disbelief of one who said that (i.e. Takfīr of a Muslim) out of misinterpretation or ignorance".
2. Whoever said it (i.e. Takfīr of a Muslim) from the way of oppression/injustice, and enmity of opposition, and accusation, while he is truly a Muwahhid inwardly, then this person is in danger.
However it doesn't appear (to mean) and Allāh (جل وعلا) knows best, that his kufr is major kufr, rather he could've fell into an enormous sin & minor kufr, and this is what the vast-majority of Scholars are upon.
3. Whoever made Takfīr upon him without a misinterpretation or misconception, so here he becomes a kāfir because he made Ēmān as Kufr, and based upon this al-Bukhārī (رحمه الله) wrote a chapter-heading:
"Whoever makes Takfīr on his brother without Ta'wīl, then he is (exactly) like what he said".
And he mentioned some textual evidences regarding this (such as) "Whoever says to his brother...(O Kāfir...till the end of the Hadīth)"
Pay attention: The difference between the first (case) and the second (case) is that the first (case) is a Ta'wīl based upon a valid (Shar'ī) misinterpretation by using evidences from the texts (Qur'ān & Sunnah), and with the purpose of establishing the truth for the sake of Allâh(سبحانه وتعالى), and ordaining the good & forbidding the evil.
But as for the second (case), then his Ta'wīl is not a valid (Shar'ī) misinterpretation, even if he used evidences from the Sharī'ah, with the purpose of enmity against his opponent, oppression/injustice and gaining victory for himself, and Allāh (جل وعلا) knows best. [1]
~ The Imām, Shaykh Nāsir al-Fahd (فك الله أسره).