Ali Bin Abi Talib (radiyAllaahu 'anhu) said:

“If this religion was according to opinion, then the bottom of the khuff (leather socks) would have more right to be wiped than its top, and I have seen the Prophet (salla Allaahu alayhi wa sallam) wipe over the top of his khuffs (leather socks).”

[Abu Dawud 162, Sahih by Albani also Irwa Ghaleel 103]

And Imam Sufyan Thawri said thrice that:

“This religion is based upon narrations, not opinion, This religion is based upon narrations, not opinion, This religion is based upon narrations, not opinion”.

 
[No.3 (1/4) Sharaf Ashaabul hadeeth. (Hussain Saleem Asad Zumri said Isnaad Sahih in the checking of Jami Bayan Ilm 2/75]