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Surah 16. An-Nahl
Ayah 101 - 102
١٠١. وَإِذَا بَدَّلْنَآ ءَايَةً مَّكَانَ ءَايَةٍ ۙ وَٱللَّهُ أَعْلَمُ بِمَا يُنَزِّلُ قَالُوٓا۟ إِنَّمَآ أَنتَ مُفْتَرٍۭ ۚ بَلْ أَكْثَرُهُمْ لَا يَعْلَمُونَ
١٠٢. قُلْ نَزَّلَهُۥ رُوحُ ٱلْقُدُسِ مِن رَّبِّكَ بِٱلْحَقِّ لِيُثَبِّتَ ٱلَّذِينَ ءَامَنُوا۟ وَهُدًى وَبُشْرَىٰ لِلْمُسْلِمِينَ
101. And when We change a verse in place of another - and Allah knows best what He reveals - they (the disbelievers) say: "You (O Muhammad) are but a forger.'' Rather, most of them know not. 102. Say (O Muhammad); "Ruh-ul-Qudus has brought it (the Qur'an) down from your Lord with truth.'' for the conviction of those who believe, and as a guide and good news for the Muslims.
Allah tells us of the weak minds of the idolators, and their lack of faith and conviction. He explains that it is impossible for them to have faith when He has decreed that they are doomed. When they saw that some rulings had been changed by being abrogated, they said to the Messenger of Allah :
(You are but a forger) meaning one who tells lies. But Allah is the Lord Who does whatever He wills, and rules as He wants.
(And when We change a verse (of the Qur'an) in place of another) Mujahid said: this means, "We remove one and put another in its place.'' Qatadah said: this is like the Ayah:
(Whatever verse We change ﴿abrogate﴾ or omit ﴿the abrogated﴾...)'' (2:106). Allah said, in response to them:
(Say: "Ruh-ul-Qudus has brought it...'') meaning, Jibril,
(from your Lord with truth, ) meaning, with truthfulness and justice
(for the conviction of those who believe,) so that they will believe what was revealed earlier and what was revealed later, and humble themselves towards Allah.
(and as a guide and good news for the Muslims.) meaning He has made it a guide and good news to the Muslims who believe in Allah and His Messengers.