Allah tells us about the idolators' lies, allegations, and slander when they claimed that this Qur'an which Muhammad had recited for them, was actually taught to him by a human. They referred to a foreign (i.e., non-Arab) man who lived among them as the servant of some of the clans of Quraysh and who used to sell goods by As-Safa. Maybe the Messenger of Allah used to sit with him sometimes and talk to him a little, but he was a foreigner who did not know much Arabic, only enough simple phrases to answer questions when he had to. So in refutation of their claims of fabrication, Allah said:

﴿لِّسَانُ الَّذِى يُلْحِدُونَ إِلَيْهِ أَعْجَمِىٌّ وَهَـذَا لِسَانٌ عَرَبِىٌّ مُّبِينٌ﴾

(The tongue of the man they refer to is foreign, while this (the Qur'an) is a (in) clear Arabic tongue.) meaning, how could it be that this Qur'an with its eloquent style and perfect meanings, which is more perfect than any Book revealed to any previously sent Prophet, have been learnt from a foreigner who hardly speaks the language No one with the slightest amount of common sense would say such a thing.

﴿إِنَّ الَّذِينَ لاَ يُؤْمِنُونَ بِآيَـتِ اللَّهِ لاَ يَهْدِيهِمُ اللَّهُ وَلَهُمْ عَذَابٌ أَلِيمٌ - إِنَّمَا يَفْتَرِى الْكَذِبَ الَّذِينَ لاَ يُؤْمِنُونَ بِآيَـتِ اللَّهِ وَأُوْلـئِكَ هُمُ الْكَـذِبُونَ ﴾

(104. Verily, those who do not believe in Allah's Ayat (signs, or revelation), Allah will not guide them, and theirs will be a painful punishment.) (105. It is only those who do not believe in Allah's Ayat who fabricate the falsehood, and it is they who are liars.) Allah tells us that He does not guide those who turn away from remembering Him and who are heedless of that which He revealed to His Messenger , those who have no intention of believing in that which he has brought from Allah. This kind of people will never be guided to faith by the signs of Allah and the Message which He sent His Messengers in this world, and they will suffer a painful and severe punishment in the Hereafter. Then Allah informs us that His Messenger is not a forger nor a liar, because the one who fabricates falsehood about Allah and His Messenger is the most evil of creatures.

﴿الَّذِينَ لاَ يُؤْمِنُونَ بِآيَـتِ اللَّهِ﴾

(Verily, those who do not believe in Allah's Ayat,) Allah will not guide them, and theirs will be a painful punishment, meaning, the disbelievers and heretics who are known to the people as liars. The Messenger Muhammad , on the other hand, was the most honest and righteous of people, the most perfect in knowledge, deeds, faith and conviction. He was known among his people for his truthfulness and no one among them had any doubts about that - to such an extent that they always addressed him as Al-Amin (the Trustworthy) Muhammad. Thus when Heraclius, the king of the Romans, asked Abu Sufyan about the attributes of the Messenger of Allah , one of the things he said to him was, "Did you ever accuse him of lying before he made his claim'' Abu Sufyan said, "No''. Heraclius said, "He would refrain from lying about people and then go and fabricate lies about Allah''

﴿مَن كَفَرَ بِاللَّهِ مِن بَعْدِ إيمَـنِهِ إِلاَّ مَنْ أُكْرِهَ وَقَلْبُهُ مُطْمَئِنٌّ بِالإِيمَـنِ وَلَـكِن مَّن شَرَحَ بِالْكُفْرِ صَدْرًا فَعَلَيْهِمْ غَضَبٌ مِّنَ اللَّهِ وَلَهُمْ عَذَابٌ عَظِيمٌ - ذلِكَ بِأَنَّهُمُ اسْتَحَبُّواْ الْحَيَوةَ الْدُّنْيَا عَلَى الاٌّخِرَةِ وَأَنَّ اللَّهَ لاَ يَهْدِى الْقَوْمَ الْكَـفِرِينَ - أُولَـئِكَ الَّذِينَ طَبَعَ اللَّهُ عَلَى قُلُوبِهِمْ وَسَمْعِهِمْ وَأَبْصَـرِهِمْ وَأُولَـئِكَ هُمُ الْغَـفِلُونَ - لاَ جَرَمَ أَنَّهُمْ فِى الاٌّخِرَةِ هُمُ الْخَـسِرونَ ﴾

(106. Whoever disbelieves in Allah after his belief - except one who was forced while his heart is at peace with the faith - but whoever opens their breasts to disbelief, on them is wrath from Allah, and theirs will be a terrible torment.) (107. That is because they preferred the life of this world over that of the Hereafter. And Allah does not guide the people who disbelieve.) (108. They are those upon whose hearts, hearing (ears) and sight (eyes) Allah has set a seal over. And they are the heedless!) (109. No doubt, in the Hereafter they will be the losers.)