Will Allah accept the repentance of a young man who believed in Him and His Messenger, then was afflicted by doubts about existence, which led to his sporadic prayer, then uttered a statement that is feared to be an insult to the Prophet (peace and blessings of Allah be upon him) out of ignorance of the ruling, and he is now content with faith?

The door of repentance is open to all. Let the repentant turn to his Lord, and let him know that Allah's pardon and mercy encompass everything, and that one who repents of a sin is like one who has no sin, even if the sin was reviling the Prophet, peace and blessings be upon him, so what if the matter is doubtful? Therefore, he must cast aside whispers and strive in obedience, for Allah is Forgiving and Merciful; no sin is too great for Him to forgive, in accordance with His saying, "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" (Az-Zumar: 53).