Musnad Ahmad 132:10

Hassan narrated to us, Ibn Lahi'ah narrated to us, he said: Zabban narrated to us, from Sahl ibn Mu'adh ibn Anas, from his father, from the Messenger of Allah, may Allah bless him and grant him peace, that he said: "The best of virtues are that you uphold ties with the one who cuts you off, you give to the one who withholds from you, and you pardon the one who insults you."