Abdullah bin Umar reported,

The Messenger of Allah ﷺ said, "If any man says to his brother, 'You disbeliever,' then one of the two has incurred it."

Bukhari 6104

Sahih

حدثنا إسماعيل قال حدثني مالك عن عبد الله بن دينار

عن عبد الله بن عمر رضي الله عنهما

أن رسول الله ﷺ قال أيما رجل قال لأخيه يا كافر فقد باء بها أحدهما

البخاري 6104صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Manners
Chapter
Whoever declares his brother a disbeliever without interpretation, he is as he said
Numbering
Darussalam 6104