Hadith
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي ابْنَ مُحَمَّدٍ - عَنِ الْعَلاَءِ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الْمُسْتَبَّانِ مَا قَالاَ فَعَلَى الْبَادِي مِنْهُمَا مَا لَمْ يَعْتَدِ الْمَظْلُومُ " .
Abu Hurairah reported the Messenger of Allah (May peace be upon him) as saying:when two men abuse one another, what they say is laid to the charge of the one who began it, so long as the one who is wronged does not go over the score
Sahih · Al-Albani
Sunan Abi Dawud 4894 ·Book 43, Hadith 122·Also available on sunnah.com·