Is saying "a person's prayer is not accepted" an assumption about Allah Almighty?

It is not permissible to definitively state that a person's prayer is not accepted unless its invalidity is known Islamically, such as one who prayed while in a state of impurity (hadath) or missed a pillar (rukn). However, if the worshipper fulfills the conditions and pillars, no one can assert with certainty whether their prayer is accepted or not, because that is related to sincerity to Allah, which is an unseen matter known only to Allah. To say that prayer is not accepted without Islamic proof is a forbidden fabrication against Allah. This is not considered "ta'alli ala Allah" (attributing things to Allah without knowledge), for "ta'alli" means to swear an oath.