• إِلْحَاد
• مُلْتَحَد
• يُلْحِدُونَ

Appears 6 times in the Quran.

1. 7:180 وَلِلَّهِ ٱلْأَسْمَآءُ ٱلْحُسْنَىٰ فَٱدْعُوهُ بِهَا وَذَرُوا۟ ٱلَّذِينَ يُلْحِدُونَ فِىٓ أَسْمَٰٓئِهِۦ سَيُجْزَوْنَ مَا كَانُوا۟ يَعْمَلُونَ

   And Allah's are the best names, therefore call on Him thereby, and leave alone those who violate the sanctity of His names; they shall be recompensed for what they did.
   

2. 16:103 وَلَقَدْ نَعْلَمُ أَنَّهُمْ يَقُولُونَ إِنَّمَا يُعَلِّمُهُۥ بَشَرٌ لِّسَانُ ٱلَّذِى يُلْحِدُونَ إِلَيْهِ أَعْجَمِىٌّ وَهَٰذَا لِسَانٌ عَرَبِىٌّ مُّبِينٌ

   And certainly We know that they say: Only a mortal teaches him. The tongue of him whom they reproach is barbarous, and this is clear Arabic tongue.
   

3. 18:27 وَٱتْلُ مَآ أُوحِىَ إِلَيْكَ مِن كِتَابِ رَبِّكَ لَا مُبَدِّلَ لِكَلِمَٰتِهِۦ وَلَن تَجِدَ مِن دُونِهِۦ مُلْتَحَدًا

   And recite what has been revealed to you of the Book of your Lord, there is none who can alter His words; and you shall not find any refuge besides Him.
   

4. 22:25 إِنَّ ٱلَّذِينَ كَفَرُوا۟ وَيَصُدُّونَ عَن سَبِيلِ ٱللَّهِ وَٱلْمَسْجِدِ ٱلْحَرَامِ ٱلَّذِى جَعَلْنَٰهُ لِلنَّاسِ سَوَآءً ٱلْعَٰكِفُ فِيهِ وَٱلْبَادِ وَمَن يُرِدْ فِيهِ بِإِلْحَادٍۭ بِظُلْمٍ نُّذِقْهُ مِنْ عَذَابٍ أَلِيمٍ

   Surely (as for) those who disbelieve, and hinder (men) from Allah's way and from the Sacred Mosque which We have made equally for all men, (for) the dweller therein and (for) the visitor, and whoever shall incline therein to wrong unjustly, We will make him taste of a painful chastisement.
   

5. 41:40 إِنَّ ٱلَّذِينَ يُلْحِدُونَ فِىٓ ءَايَٰتِنَا لَا يَخْفَوْنَ عَلَيْنَآ أَفَمَن يُلْقَىٰ فِى ٱلنَّارِ خَيْرٌ أَم مَّن يَأْتِىٓ ءَامِنًا يَوْمَ ٱلْقِيَٰمَةِ ٱعْمَلُوا۟ مَا شِئْتُمْ إِنَّهُۥ بِمَا تَعْمَلُونَ بَصِيرٌ

   Surely they who deviate from the right way concerning Our communications are not hidden from Us. What! is he then who is cast into the fire better, or he who comes safe on the day of resurrection? Do what you like, surely He sees what you do.
   

6. 72:22 قُلْ إِنِّى لَن يُجِيرَنِى مِنَ ٱللَّهِ أَحَدٌ وَلَنْ أَجِدَ مِن دُونِهِۦ مُلْتَحَدًا

   Say: Surely no one can protect me against Allah, nor can I find besides Him any place of refuge: