It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "Whatever two people who abuse each other say, its sin is upon the one who started it, as long as the oppressed does not exceed the limits."
Hadith Referenceالادب المفرد / كتاب السباب / 423
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه مسلم ، كتاب البر و الصلة والأدب : 68 ، 2587 و أبوداؤد : 4894 و الترمذي : 1981 - انظر الصحيحة : 570»