Surah Ar-Ra'd 13:43

وَيَقُولُ ٱلَّذِينَ كَفَرُوا۟ لَسْتَ مُرْسَلًا ۚ قُلْ كَفَىٰ بِٱللَّهِ شَهِيدًۢا بَيْنِى وَبَيْنَكُمْ وَمَنْ عِندَهُۥ عِلْمُ ٱلْكِتَـٰبِ

And those who have disbelieved say, "You are not a messenger." Say, [O Muḥammad], "Sufficient is Allāh as Witness between me and you, and [the witness of] whoever has knowledge of the Scripture."

Translation: Saheeh International

Tafsir

And those who disbelieve say to you ‘You have not been sent by God!’ Say to them ‘God suffices as a witness between me and you to my truthfulness as a messenger and he who possesses knowledge of the Book’ from among the Christian and Jewish believers.

Excerpt from Tafsir al-Jalalayn, commentary on 13:43, via Quran.com. The reader has the full commentary and 9 more tafsirs.