Below is a law from Islamic law of Ayatollah Sistani. As per the law, if i pray namaz while cat hair is on my dress or body , my namaz will become void?

833. If the saliva, or water from the nose, or any other moisture, from an animal whose meat is haraam to eat, like that of a cat, is on the body or the dress of a person in namaz, and if it is wet, the namaz will be void. But if it has dried up, and if its substance has been removed, then the prayer is valid.

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Walaikumussalam
Yes if you read last sentence then you will understand it is clearly mentioned that :
But if it has dried up, and if its substance has been removed, then the prayer is valid.
If is dried up and substances removed then prayer is void
Wassalam