What is the criterion for declaring a specific person a disbeliever

Question:
What is the criterion for declaring a specific person a disbeliever, when some scholars say that one should not declare a person a disbeliever, even if he is a specific Jew, until it is confirmed that he died in a state of disbelief?

Answer:
This is a confusion, may Allah protect us from it. A disbeliever is declared a disbeliever; one rules that he is a disbeliever if he displays disbelief. If he associates partners with Allah, one rules that he is one who associates partners with Allah. However, one does not assert that he is in the Fire. There is a difference between asserting that someone is in the Fire and ruling that he is a disbeliever. You rule that he is a disbeliever based on what he has done. As for the Hereafter, you do not rule that a specific person is among the people of the Fire. He may have repented and you did not know, or he may have died in a state of repentance and you did not know. This person who is speaking is mixing up the two matters. He is mixing up the issue of declaring someone a disbeliever with the issue of ruling that a specific person is in the Fire.