Waalaikumsalam
Knowledge and believing might be same matter (my English is not perfect).

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Yes in the worldly matter. But in the matter of faith, "know" and "believe" are two different things which "know" is coming from "believe".
We have never seen Allah, but we know that Allah does exist because we believe. If we don't believe in Allah, then we would never know that Allah does exist.
I'll tell a true story.
One day when I was young, me and my friend visited a cafe, and we saw a guy who we knew. He was in debate with two hijabi sisters. That guy said that Allah does not exist, while those hijabi said that Allah does exist. They tried to convince him with Qur'an, with signs in nature, etc. But that guy just shake his head. Then he put a bottle on the table and told them "I know this bottle does exist because I can see it. Now tell me, how can I believe that Allah does exist if I cannot see Him?". Those hijabi could not say anything, and then they left him.
Me and my friend moved to his table and welcomed by him with "I don't believe something that I cannot see it". My friend asked him "You can think, but can you see mind?". That guy replied with quoted Descartes "I think, therefore I am". My friend could not say anything. And a moment later that guy left us with a winning smile on his face.
I never heard about him again until few years ago when my another friend who active in Islamic activities told me that he often meet that guy, and he has changed.
Few days later I read a short article about that guy in my local newspaper where he wrote few poems. I was so surprised because those poems were Islamic religious poems.
I still remember when he said he could not believe anything that he could not see. But then Allah gave him an Iman that made him believe and know the existence of Allah although he could not see Allah.