﴿ لَّٰكِنِ ٱللَّهُ يَشْهَدُ بِمَآ أَنزَلَ إِلَيْكَ ۖ أَنزَلَهُۥ بِعِلْمِهِۦ ۖ وَٱلْمَلَٰٓئِكَةُ يَشْهَدُونَ ۚ وَكَفَىٰ بِٱللَّهِ شَهِيدًا ﴾

“However it be, God [Himself] bears witness to the truth of what He has bestowed from on high upon thee: out of His own wisdom has He bestowed it from on high, with the angels bearing witness thereto - although none can bear witness as God does.”

Then Allah revealed about the people of Mecca when they said to the Prophet: we have asked the people of the Book about you and none of them testifies that you are a prophet sent by Allah, by saying: (But Allah (Himself) testifieth) even if no one else testifies (concerning that which He hath revealed unto thee) the Qur'an that Gabriel brought you; (in His knowledge) by His command (hath He revealed it; and the Angels also testify) testify to this. (And Allah is sufficient Witness) even if no one else besides Him testifies.