Is it possible that God—and refuge is sought in God—would not be truthful in His threat of resurrection, Paradise, and Hell, despite His absolute power? Can the intellect believe that, even with a weak probability? And does the hadith attributed to 'Umar indicate the permissibility of this possibility, knowing that God says: "And worship your Lord until there comes to you the certainty" (Al-Hijr: 99)? Does this mean that complete certainty cannot be attained in this world?

Certainty is a condition for the validity of faith, for faith is not valid with doubt and suspicion. Believers do not doubt, whereas the doubter is among the hypocrites. Doubt concerning the fundamentals of faith is a cause for disbelief, unless it is a whisper (waswasah) that does not settle in the heart and is disliked by the believer; this is indeed pure faith.

The circulated story about Imam Ali, may Allah be pleased with him, in addressing one who doubts the Last Day, if authentic, is in the context of argumentation and debate to compel the opponent, and not to build faith on mere possibility.

As for the Almighty’s saying: {And worship your Lord until there comes to you the certainty} (Quran 15:99), certainty here refers to death.