«أيما امرئ قال لأخيه: كافر فقد باء بها أحدهما إن كان كما قال وإلا رجعت إليه»
The Prophet (peace and blessings be upon him) said:
"Whoever calls his (Muslim) brother a disbeliever, then one of the two of them has returned with it (disbelief): if he (the one called a disbeliever) is as he said (then so be it); otherwise it (the verdict of disbelief) will return to the one who said it."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 2698