﴿ 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.”

Please check ayah 4:170 for complete tafsir.