´'Abu Hurairah narrated that the Messenger of Allah said:` "(The burden of) what is said by the two who vilify each other is upon the one who initiated it, as long as the one who was wronged does not transgress."
Hadith Referenceسنن ترمذي / كتاب البر والصلة عن رسول الله صلى الله عليه وسلم / 1981