08-31-2018, 08:53 PM
As-Salaam alaikum,
Sayyadina Abdullah Ibn Mas'ud, may Allah be pleased with him, narrated that the Prophet, Sallallahu alaihi Wasallam, said:--
"I am the city of knowledge, Abu Bakr is its foundation, Umar is its wall,
Usman is its roof and Ali is its portal [gate]." [Musnad-ul-Firdau, vol. 1 Hadith No. 105].