Sahih Bukhari Volume 8, Book 73, Hadith Number 147.

Narated By ‘Aisha : Whenever Allah’s Apostle was given the choice of one of two matters he would choose the easier of the two as long as it was not sinful to do so, but if it was sinful, he would not approach it. Allah’s Apostle never took revenge over anybody for his own sake but (he did) only when Allah’s legal bindings were outraged, in which case he would take revenge for Allah’s sake.” (See Hadith No. 760. Vol. 4)