How can one reconcile the idea that sins may prevent prayers from being answered—as in the Hadith, "How can he be answered?"—with Allah's answering of Iblis's prayer—as in the verse: (He said, "Indeed, you are among those reprieved")—knowing that all people have sins?

For a supplication to be answered, there are conditions and causes. Sins prevent its acceptance, but they do not make it impossible. Indulging in unlawful acts and consuming forbidden foods may hinder the answer, as does neglecting duties like enjoining good and forbidding evil, which prevents the supplication of the righteous from being answered. Performing acts of obedience necessitates the answering of supplications. Allah answered Iblis despite his disbelief. The answering of a supplication occurs in one of three ways: either the request is granted expeditiously in this world, or it is stored for the Hereafter, or an equivalent amount of evil is averted from the person.