What is the ruling on someone who said to another during a quarrel: "By Allah, I will not leave you, even if the Prophet comes," intending thereby the impossibility of leaving his opponent, not to insult or disparage the Prophet, then repented and reformed his ways? Is he a Muslim? Are his acts of worship accepted? And is he considered a martyr if he strives in jihad and dies?

This statement is reprehensible and should not emanate from a Muslim. However, it does not amount to disbelief merely by itself, as it is not an explicit disparagement of the Prophet, peace and blessings be upon him. This brother has repented, and repentance demolishes what came before it. Allah forgives all sins through repentance, as He Almighty said: "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).