Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) said: "Take my advice to treat my uncle al-Abbas well, for he is the remnant of my forefathers, and a man's uncle is like (a branch from the same root as) his father."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11061