Whenever the hour of salaah would approach, Rasulullah (sallallahu ‘alaihi wasallam) would perform his salaah secretly in a valley or mountain pass.
On one occasion, Rasulullah (sallallahu ‘alaihi wasallam) was performing his salaah with Hazrat ‘Ali (radhiyallahu ‘anhu) in a certain mountain pass when Abu Taalib suddenly came their way. Until that time, Hazrat ‘Ali (radhiyallahu ‘anhu) had not revealed his Islam to his parents, uncles and other relatives. Abu Taalib addressed Rasulullah (sallallahu ‘alaihi wasallam) asking, “O nephew! What religion is this? What kind of worship is this?”
Rasulullah (sallallahu ‘alaihi wasallam) replied, “Uncle! This is the Deen of Allah Ta‘ala, His angels and all His prophets, especially the Deen of our forefather, Hazrat Ebrahim (‘alaihis salaam). Allah Ta‘ala has made me His Rasul and deputed me to all His servants. You are most deserving of my advice. I invite you towards goodness and divine guidance. You, before anyone else, should accept this divine guidance and true religion and give me assistance and support in Deen.”
Abu Taalib replied, “Nephew! I cannot renounce the religion of my forefathers, but I assure you that nobody will harm you.”
He then turned to Hazrat ‘Ali (radhiyallahu ‘anhu) asking, “Son! What is this religion that you have chosen?” Hazrat ‘Ali (radhiyallahu ‘anhu) replied, “Father! I have brought Imaan in Allah Ta‘ala and His Rasul (sallallahu ‘alaihi wasallam) and I believe in whatever he conveys to us from Allah Ta‘ala. I worship Allah Ta‘ala with him and I am his devoted follower.” Abu Taalib remarked, “This is the best for you. He has invited you to pure goodness. Don’t leave him and don’t abandon him.”
(Extracted from Seeratul Mustafa 1/160)