It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyiduna Abu Bakr (may Allah be pleased with him) had a particular seat in the gathering of the Messenger of Allah (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 Sayyiduna al-Abbas (may Allah be pleased with him) came, and Sayyiduna Abu Bakr (may Allah be pleased with him) moved away from his place for him. the Messenger of Allah (peace and blessings be upon him) asked him: "What is the matter with you?" He said: "O Messenger of Allah! Your uncle has come." So the Messenger of Allah (peace and blessings be upon him) looked at him, then turned smiling to Sayyiduna Abu Bakr (may Allah be pleased with him) and said: "Here is al-Abbas coming, wearing white clothes; after him his descendants will wear black, and twelve men from among them will become rulers." Then, when Sayyiduna al-Abbas (may Allah be pleased with him) arrived, he said: "O Messenger of Allah! What did you say to Abu Bakr?" He (peace and blessings be upon him) said: "I said nothing but good." He said: "You have spoken the truth, may my father and mother be sacrificed for you; you say nothing but good." He (peace and blessings be upon him) said: "I said: My uncle has come, wearing white clothes; after him his descendants will wear black, and twelve men from among them will become rulers."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Ishaq (may Allah have mercy on him) except Hafs (may Allah have mercy on him), and Muhammad bin Salih (may Allah have mercy on him) is alone in transmitting it."
Hadith Referenceالمعجم الأوسط / باب الألف / 590
Hadith Gradingمحدثین:إسناده ضعيف، فيه جماعة لم يُعرفوا
Hadith Takhrij«قال الهيثمي: فيه جماعة لم أعرفهم «مجمع الزوائد ومنبع الفوائد، ج 9، ص 270»» «أخرجه الطبراني فى «الكبير» برقم: 10675»