(183) بَابُ إِصْلاحِ ذَاتِ الْبَيْنِ
Abu'd-Darda' reported that the Prophet, may Allah bless him andgrant him peace, said, "Shall I tell you a degree better than prayer, fastingand sadaqa?" "Yes," they replied. He went to say, Improving a state offriendship. Causing discord in a state of friendship is what shaves thingsaway."
Reference: Al-Adab Al-Mufrad 391
In-book reference: Book 21, Hadith 7
English translation: Book 21, Hadith 391