If an object like an article of clothing becomes najis (impure) and thereafter a person doubts whether or not they have properly made it tahir (ritually clean) can he or she assume it is tahir (pure)?
An object, like an article of clothing, that is known to have become impure is termed mutanajjis (made impure), and its general rule is that if its tathir (purification) is in doubt (i.e. not sure), it will still be considered najis (impure).