Evil thoughts are not harmful to faith and there will be no punishment on them

(54) It is related by Abu Hurairah that the Apostle of God said: “God has forgiven my followers evil thoughts and misgivings and there will be no punishment on them until they are acted upon or uttered by the tongue.”
-Bukhari and Muslim
Commentary.-Sometimes most filthy ideas assail a man's heart and skeptical and atheistic questions arise in his mind. In this Tradition the assurance is given that as long as these desires, notions, doubts or fears remain confined to thought and feeling, there will be no punishment on them from God. But if they are given expression to, by word or deed, Divine chastisement will, of course, follow.
(55) Narrates Abdullah bin Abbas that, once, a person came to the Prophet and said, “Sometimes such wicked ideas come to my mind that I would prefer to be burnt down and reduced to charcoal than to give utterance to them.” The Prophet replied, “Praise be to Allah who turned back the matter towards thought sentiment.”
-Abu Dawood
Commentary.-The questioner is advised here not to eat his heart out but be grateful to God that, out of His grace, He protected his inmost self against adopting and accepting the vicious notions and desires and did not allow them to go beyond the realm of thinking and feeling.
(56) It is related by Abu Hurairah that, once, some Companions presented themselves before the Apostle of God and said, “Our condition is that sometimes we experience such evil thoughts and sentiments in our heart that it is most painful even to mention them.” “Is it really so?” inquired the Prophet. “Yes”, replied the Companions, “This is our condition.” “But that is pure Faith,” the Prophet exclaimed.
-Muslim
Commentary.-It shows that to feel so greatly distressed at notions that are contrary to Islam and the Shariat that it may be intolerable even to bring them on the tongue is a mark of the purity of Faith.
(57) It is related by Abu Hurairah that the Apostle of God said: “Occasionally, Satan comes to you and asks, ‘Who created this thing [and] who created that thing,' It goes on like that till about God Himself he sows the doubt in your hearts [that when everything has been created by someone] who is His creator? So when this stage is reached the bondsman should seek the refuge of the Lord and stop."
-Bukhari and Muslim
Commentary.-It shows that such ideas and misgivings are the handiwork of Satan and when he causes a doubt concerning the very existence of the Lord to crop up in anyone's heart the best course for him is to beg the protection of God against the mischief of the Devil and divert his mind from it. When the existence of Allah is an Attribute of His Being and He is the Creator of all things a question like this does not arise about Him in the least degree.
(58) It is related by Abu Hurairah that the Apostle of God said: “Vain questions and aimless arguments will go on among the people till the foolish question will also be asked that when God created all things, by whom was He created? So, anyone who is confronted with it should put an end to the discussion by declaring, ‘I believe in God and His Apostles.'”
-Bukhari and Muslim
Commentary.-The attitude of a faithful Believer to such ideas and inquiries should be that he plainly told the questioner, the doubt-instilling Satan and his own inmost self that the light of faith in God and His Apostle had reached him, and, therefore, the afore-mentioned question was not worthy of his consideration just as it was senseless for a clear-eyed person to think or discuss logically whether the sun was bright or not.