Hadith No: 3
Al-Heithami - Majma' al-Zawa'id wa Manba' al-Fawa'id - Book of Virtues
Chapter on the Virtues of Ali ibn Abi Talib (peace be upon him) - A Comprehensive Chapter on His Virtues (peace be upon him)
Volume: (9) - Page Number: (120)
[The text is lengthy, so only the relevant excerpt is provided here]
14696 - From Amr ibn Maymun - meaning al-Awdi - who said: I was sitting with Ibn Abbas when nine men approached him and said: "O Ibn Abbas, either you stand with us, or let these people leave us." Ibn Abbas replied: "Rather, I will stand with you," and he was in good health that day, before he became blind....
He said that Abu Bakr closed the doors of the mosque, except for the door of Ali. He said Ali could enter the mosque while in a state of janabah (major ritual impurity), and this was his only way, as he had no other route.