Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated: Sayyiduna Abu Bakr (may Allah be pleased with him) had a seat near the Prophet (peace and blessings be upon him) from which he would rise only for Sayyiduna al-Abbas (may Allah be pleased with him), and this pleased the Messenger of Allah (peace and blessings be upon him). One day al-Abbas (may Allah be pleased with him) came, and Abu Bakr (may Allah be pleased with him) moved from his place to make room for him. The Messenger of Allah (peace and blessings be upon him) said: "What is the matter with you?" He said: "O Messenger of Allah, your (peace and blessings be upon him) uncle is coming." The Messenger of Allah (peace and blessings be upon him) looked at him, then turned to Abu Bakr (may Allah be pleased with him) smiling and said: "This is al-Abbas, coming wearing white clothes, and after him his descendants will wear black, and twelve men from among them will rule."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10629