I have a Muslim friend who is not convinced with the religion. Whenever I have a discussion with him he says, “How do you know that Islam is the true religion? I need a realistic proof other than the old stories.” He is not convinced with my words. I want an answer from your eminence so that he might return to guidance.
May you always be under the care of Allah!

And upon you be peace, together with the mercy and blessings of Allah. This person is not a believer. He is rather one of those concerning whom Allah said, “And whose hearts have a doubt. Thus they waver in their doubt.” [9:45] We seek refuge with Allah from such a condition.
As for convincing him, he should be directed to consider the miracles of the Prophet (peace and blessings be upon him) and to ponder on the open book of the universe, which includes all the creatures of this universe, and on the written Book, which is the readable revelation, and the miracles and clear verses it includes. Through this consideration and reflection he will, eventually, reach faith and will know that he was not created by no-one. Almighty Allah said, “Or were they created out of nothing? Or were they the creators [of themselves]? Or is it that they are the ones who created the heavens and the earth? Rather, they have no certainty.” [52:35-35] It is He who created man, “And [they (the signs) are all] within yourselves as well. Can you not see?” [51:21] and created the surrounding environment, including celestial bodies, heavens, the sun, the moon, the earth on which we live, the air we breathe and all the benefits of the earth. Of course, this Great Creator is not part of this universe.
One who considers the miracles of the prophets that Allah gave them, including the miracles of the Seal of the prophets (peace and blessings be upon him), knows for sure that they are from Almighty Allah. The most important thing for this person is to consider the scientific miracles of the Quran and the Sunnah. Had the Quran been from other than Allah, it would not have included, for example, the phases of the embryo. Almighty Allah said, “Verily, We created man out of an extraction of mud. Then We made him a sperm-drop set in a well-established place. Then We created the sperm-drop into a clinging clot. Then We created the clinging clot into a morsel-like lump. Then We created, from the morsel-like lump, bones. Then We clothed the bones with flesh. Thus do We bring him forth as an entirely different creation. So blessed be Allah the best of creators.” [23:12-14] How could the Quran have talked so clearly and explicitly about these four phases that scholars came to know about only in contemporary time had it not been from other than Almighty Allah?
Moreover, many of the verses of the Quran are related to the scientific miracles, such as the verse of sending down iron, “And We sent down iron in which there is a mighty force, and [in which there are] many benefits for all people.” [57:25] Scientifically, it has been proven that iron was not made in the earth but rather in another place. Also add to this the description of the Prophet (peace and blessings be upon him) found in the old Scriptures and how he managed to amend souls and hearts, and to guide a misguided and lost nation.
All these are miracles that he has to revise and consider. He needs to read the Quran and reflect on it, to attend scholars’ sessions, and to ponder on the past and the future of his life and on his destiny. We mention all this in brief; and if we wanted to explain all the miracles and verses, this would take a long time. This amount is enough. We advise this person to seek guidance from Almighty Allah, “Whomever Allah guides, then he is truly guided. But whomever He leaves to stray, then never shall you find for him any rightly guiding patron” [18:17] “Indeed, you cannot guide all those whom you love [to Islam]. Rather, it is Allah who guides whomever He so wills.” [28:56] Let him ponder on the verses of Almighty Allah and sit with scholars to ask them about the doubts of his heart. He should also review Dala’il al-Nubuwwah by al-Bayhaqy which is a book that contains many of the miracles of the Prophet (peace and blessings be upon him). About the origin of iron, he should consult the results of the scientific miracles of the Quran published by the Society of the Miracles of the Quran. Such results are many and leave no doubt that the Quran is not from a human being but rather from Almighty Allah. This is all we can say now. As I said, he should go and sit with scholars, pray to Almighty Allah, and ask His guidance.