Praise be to Allah.
The Muslim should praise Allah, may He be exalted, and thank Him for the blessing of Islam and right guidance, for it is the greatest of blessings, as Allah, may He be exalted, says (interpretation of the meaning):
“Is he who was dead (without Faith by ignorance and disbelief) and We gave him life (by knowledge and Faith) and set for him a light (of Belief) whereby he can walk amongst men, like him who is in the darkness (of disbelief, polytheism and hypocrisy) from which he can never come out? Thus it is made fair-seeming to the disbelievers that which they used to do”
“Is he whose heart Allah has opened to Islam, so that he is in light from His Lord (as he who is non-Muslim)? So, woe to those whose hearts are hardened against remembrance of Allah! They are in plain error!”
“And had it not been for the Grace of Allah and His Mercy on you, not one of you would ever have been pure from sins. But Allah purifies (guides to Islam) whom He wills”
If this Muslim looks at the world around him and reflects upon what the people of polytheism and idolatry, such as the Christians and others, follow, he will realise the greatness of the blessing that Allah has bestowed upon him.
Yet despite that, the Muslim may experience some doubts, because of his lack of knowledge or weakness of faith, or because there is someone who tries to make him doubt. In that case, he has to dispel the doubt by asking people of knowledge, and reflecting upon the words of Allah, may He be exalted, and the words of His Prophet (blessings and peace of Allah be upon him), and by studying the Seerah (Prophet’s biography) and signs and miracles, for these are things that will increase his faith and bring him peace of mind and reassurance.
There is nothing wrong with asking about a miracle and how sound it is, so as to increase one’s certainty and steadfastness. Asking such questions is not regarded as going beyond the bounds of Islam, but he should beware of persisting in doubts or stopping good deeds, such as giving up prayer – Allah forbid – because giving up prayer constitutes disbelief (and puts a person beyond the bounds of Islam), according to the more sound of the two scholarly opinions.
The Muslim should understand that no matter what sins he may commit, if he then repents and seeks forgiveness, Allah, may He be exalted, will forgive him no matter what his sins are. Allah, may He be exalted, turned in mercy to people who had lived all their lives in disbelief, polytheism and barring people from the path of Allah, then they became leaders of guidance, lights that illuminated the darkness and beacons on the path of truth and righteousness. Allah, may He be exalted, says (interpretation of the meaning):
“Know they not that Allah accepts repentance from His slaves and takes the Sadaqat (alms, charities) and that Allah Alone is the One Who forgives and accepts repentance, Most Merciful?”
“And He it is Who accepts repentance from His slaves, and forgives sins, and He knows what you do”
No matter how great the sin, Allah’s mercy, forgiveness and generosity are greater.
The poet spoke well who said:
O Lord, although my sins are great and many, I know that Your forgiveness is greater
If it be the case that only doers of good can hope for Your grace, then who could the sinner turn to for mercy?
Our advice to the one who is faced with doubts is that he should turn to the Book of Allah, may He be exalted, for it is a remedy and a healing, as Allah, may He be glorified, says (interpretation of the meaning):
“And We send down from the Quran that which is a healing and a mercy to those who believe (in Islamic Monotheism and act on it), and it increases the Zalimoon (polytheists and wrong-doers) nothing but loss”
So let him turn to Allah, calling upon Him and hoping that He will remove his worry, relieve his distress, illuminate his heart and free him from the tricks of the Shaytaan.
If his doubt is based on a particular specious argument, let him ask the scholars about it, for the religion of Islam is so great and strong that no specious argument can stand up to it or resist it.
If what he is dealing with is a kind of waswasah (whispers from the Shaytaan) that is not based on a particular argument, then the remedy for that is remembering Allah (dhikr), doing acts of obedience and worship, seeking refuge with Allah, keeping busy and ignoring it. See question no. 12315.
We ask Allah to help us all to do that which He loves and which pleases Him.
And Allah knows best.