Sahih Bukhari Volume 006, Book 060, Hadith Number 187.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 60. Prophetic Commentary on the Qur'an (Tafseer of The Prophet (PBUH))
Narrated By Ibn Abi Mulaika : There was a disagreement between them (i.e. Ibn 'Abbas and Ibn Az-Zubair) so I went to Ibn 'Abbas in the morning and said (to him), "Do you want to fight against Ibn Zubair and thus make lawful what Allah has made unlawful (i.e. fighting in Meccas?" Ibn 'Abbas said, "Allah forbid! Allah ordained that Ibn Zubair and Bani Umaiya would permit (fighting in Mecca), but by Allah, I will never regard it as permissible." Ibn Abbas added. "The people asked me to take the oath of allegiance to Ibn AzZubair. I said, 'He is really entitled to assume authority for his father, Az-Zubair was the helper of the Prophet, his (maternal) grandfather, Abu Bakr was (the Prophet's) companion in the cave, his mother, Asma' was 'Dhatun-Nitaq', his aunt, 'Aisha was the mother of the Believers, his paternal aunt, Khadija was the wife of the Prophet , and the paternal aunt of the Prophet was his grandmother. He himself is pious and chaste in Islam, well versed in the Knowledge of the Quran. By Allah! (Really, I left my relatives, Bani Umaiya for his sake though) they are my close relatives, and if they should be my rulers, they are equally apt to be so and are descended from a noble family.