Ruling on reading the books of Ahl al-Kitaab and debating with them on the internet
Question

My worry is the propogation of false notions about quran by some christians through internet.i even sent a mail to the so called muslim to christians about their fabricated stories.i want to know what should be our response regarding alkexander the great whom they say according to history died young at 33 and in koran it states that he died at a ripe old age.
Praise be to Allah.It is not permissible to read the specious arguments that the Christians propagate on the internet or via other media, or to engage with them in religious disputes and debates, except for those who are qualified to do so, who have proof and evidence and who know how to present arguments. A number of scholars have stated that it is haraam to look at any of the books of the People of the Book, except for those who have deep knowledge, because we are commanded neither to believe nor disbelieve what they tell us about stories that are not present in our religion. There is no guarantee that the ordinary person who has no knowledge will not end up believing in falsehood and rejecting the truth. Moreover, man is weak and specious arguments may take root in the heart and it may be difficult to get rid of them. The following fatwa was issued by the Standing Committee: 
“A great deal of distortion, addition and subtraction has befallen the previous divinely-revealed scriptures, as Allah has stated, so it is not permissible for a Muslim to read them and study them, unless he is one who has deep knowledge and is seeking to explain the distortions and contradictions therein.” (3/311). 
So whatever Christian books have come to you, you must hasten to get rid of them. 
With regard to what you say about Alexander the Great, this is a specious argument which is indicative of the stupidity and ignorance of the Christians. We may respond to that from several angles, as follows: 
1 – There is no mention in the Qur’aan of how long Dhu’l-Qarnayn (Alexander) lived, or of the era in which he lived. 
2 – Dhu’l-Qarnayn who is mentioned in the Qur’aan is not Alexander the Macedonian or Greek who built Alexandria. This Alexander is the one who died at the age of 33, as mentioned in the Christian books. He lived 323 years before the birth of the Messiah (peace be upon him). 
Dhu’l-Qarnayn who is mentioned in the Qur’aan lived at the time of Ibraaheem (peace be upon him), and it is said that he became Muslim at the hands of Ibraaheem (peace be upon him), and he went on pilgrimage to the Ka’bah walking. The scholars differed concerning him, as to whether he was a Prophet or a righteous slave and just king, but they agree that he was a Muslim, a monotheist (believer in Tawheed) and one who was obedient to Allah. 
The correct view is to refrain from stating what he was, because the Prophet (peace and blessings of Allah be upon him) said: “I do not know whether Tubba’ was a Prophet or not, and I do not know whether Dhu’l-Qarnayn was a Prophet or not.” 
(Narrated by al-Haakim and al-Bayhaqi; classed as saheeh by al-Albaani in Saheeh al-Jaami’, no. 5524). 
3 – The difference between this righteous slave, and the Macedonian Alexander who was a kaafir, is well known to Muslim scholars. Ibn Katheer (may Allah have mercy on him) said in al-Badaayah wa’l-Nahaayah (1/493): 
“It was narrated that Qutaadah said: Alexander was Dhu’l-Qarnayn and his father was the first of the Caesars, and he was one of the descendants of Saam ibn Nooh (Shem the son of Noah). As for Dhu’l-Qarnayn, he was Alexander son of Philip… ibn Roomi ibn al-Asfar ibn Yaqaz ibn al-‘Ees ibn Ishaaq ibn Ibraaheem al-Khaleel. This is the genealogy of him given by al-Haafiz ibn ‘Asaakir in his Taareekh. (He is known as) the Macedonian, the Greek, the Egyptian, builder of Alexandria, on the events of whose life the Greeks based their calendar. He came much later than the first Alexander. This was approximately three hundred years before the Messiah. The philosopher Aristotle was his minister and he is the one who killed Daar ibn Daar (Darius) and humiliated the kings of Persia and invaded their land. 
We have drawn attention to him because many people think that they are one and the same and that the one who is mentioned in the Qur’aan is the one whose minister was Aristotle, which has resulted in a lot of mistakes and far-reaching corruption. The former was a righteous believing slave and a just king, and the latter was a mushrik and his minister was a philosopher. There were more than two thousand years between the two, so what comparison can there be between them? They are not alike at all and they have nothing in common, except in the mind of a fool who does not know anything.” 
4 – The Christians have no information in their holy book about the second Alexander, let alone the first. All they have is the story of the visions of Daniel, which they claim refer to the rule of this infidel Alexander, and the division of his kingdom after his death. 
5 – If we assume that there is a difference between what the Qur’aan says and what their book says about a person or an event, why should that be regarded as strange? There are many such differences, especially in the stories of the Prophets such as Ibraaheem (Abraham), Nooh (Noah), Loot (Lot), Moosa (Moses), Dawood (David) and ‘Eesa (Jesus) (peace be upon them). The Christians have no reliable and continuous chain of narration for this book in which they believe, and they know nothing about those who translated it. Moreover it contains dozens of contradictions which effectively nullify any claim to infallibility or to have been written with inspiration from the Holy Spirit. It is sufficient to note the contradictions in the genealogy of Jesus (peace be upon him)! 
So how can we take what is in these distorted books as a standard by which to judge the Holy Qur’aan which is preserved by Allah?!
 And Allah knows best.