What is the conclusive material proof of the truth of Islam for someone who doubts?

The Glorious Qur’an is the luminous proof and conclusive evidence of the truth of Islam. It is the eternal miracle bestowed upon the Prophet Muhammad, peace and blessings be upon him. The Prophet alluded to this by saying: "Indeed, what I was given was a revelation which Allah revealed to me." The Qur’an itself confirms this in the words of Allah Almighty: "Is it not sufficient for them that We have sent down to you the Book which is recited to them? Indeed in that is a mercy and a reminder for a people who believe." Al-Sa'di explained that the Qur'an is sufficient as proof of the Messenger’s truthfulness because he brought it while being unlettered, and humanity was unable to challenge it, and its appearance was public, and it informed of unseen matters, and it superseded previous scriptures, and it guided to the straight path, and it is suitable for every time and place. The questioner should ponder and study the Book of Allah, and pay attention to the verses of scientific miracles within it.