Sayyiduna Anas (may Allah be pleased with him) reports this saying of the Prophet (peace and blessings be upon him): "Whatever two people who revile each other say, its burden falls upon the one of them who started it, as long as the wronged one does not transgress."
Abu Ya'la recorded it from his teacher Abu Ali, and I do not know him. The remaining narrators of this report have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 13024