Hadith 650:6
'Affan narrated to us, Hammam narrated to us, Qatadah narrated to us, from Yazid, the brother of Mutarrif, from 'Iyad ibn Himar, that the Prophet (peace and blessings of Allah be upon him) said: "The sin of the two who revile each other is upon the one who began, as long as the oppressed does not transgress, or as long as the oppressed does not transgress."
حدثنا عفان، حدثنا همام، حدثنا قتادة، عن يزيد أخي مطرف، عن عياض بن حمار ، أن النبي صلى الله عليه وسلم، قال: " إثم المستبين ما قالا على البادئ حتى يعتدي المظلوم، أو ما لم يعتد المظلوم "