Surat An-Nahl (105-106)

{إِنَّمَا يَفْتَرِي الْكَذِبَ الَّذِينَ لاَ يُؤْمِنُونَ  بِآيَاتِ اللّهِ وَأُوْلئِكَ هُمُ الْكَاذِبُونَ} (النحل: 105 )

105- The Messenger of Allah is truthful and trustworthy who does not lie, but those who lie are polytheists and atheists who disbelieve in the clear signs of Allah and His truthful miracles; those are the true liars as long as they lie in things which are clear.

{مَن كَفَرَ بِاللّهِ مِن بَعْدِ إيمَانِهِ إِلاَّ مَنْ أُكْرِهَ وَقَلْبُهُ مُطْمَئِنٌّ بِالإِيمَانِ وَلَكِن مَّن شَرَحَ بِالْكُفْرِ صَدْراً فَعَلَيْهِمْ غَضَبٌ مِّنَ اللّهِ وَلَهُمْ عَذَابٌ عَظِيمٌ} (النحل: 106 )

106- A true believer is the one who disbelieved after he had seen the light of faith, his heart became assured with it, and embraced Islam then averted preferring worldly life to the Hereafter and preferring disbelief to faith. People who are tried in their religion, tortured, and forced to disbelief but their hearts are full of faith and the love of Allah and His Messenger, those are the true believers even if they utter words of disbelief under torture and compulsion.

A clear disbeliever is the one who opened his chest to disbelief and accepted it voluntarily, such people incur the wrath of Allah and they shall have a great torment on the Day of Resurrection because of their serious crimes.

The Ayah was revealed concerning `Ammar ibn Yasir who was tortured by polytheists and was forced to utter the words of disbelief, whereas his heart is full of faith.