Sunan Abu Dawud
4894
Sahih+3

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

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid