وَيَقُولُ ٱلَّذِينَ كَفَرُوا۟ لَسْتَ مُرْسَلًا ۚ قُلْ كَفَىٰ بِٱللَّهِ شَهِيدًۢا بَيْنِى وَبَيْنَكُمْ وَمَنْ عِندَهُۥ عِلْمُ ٱلْكِتَـٰبِ
Asad Quran Translation
And [if] they who are bent on denying the truth say [unto thee, O Prophet], "Thou hast not been sent [by God]", say thou: "None can bear witness between me and you as God does; and [none can bear witness as does] he who truly understands this divine writ."84
Lit., "and anyone who possesses (man 'indahu) knowledge of the revelation" - implying that a true understanding of the Qur'an unavoidably leads one to the conviction that it has been revealed by God.
Malik Quran Translation
The unbelievers say: "You are no Rasool." Say: "Allah is all-sufficient witness between me and you, and so are those who have knowledge of the Book."
Yusuf Ali Quran Translation
The Unbelievers say: "No apostle art thou." Say: "Enough for a witness between me and you is Allah and such as have knowledge of the Book." 1867 1868
The enemies of Islam have to acknowledge that Al-Mustafawas a great and noble character, but they deny his Prophethood. He could point to his credentials from Allah in the work which he achieved, and the Qur-an which he brought.
That is, those who have knowledge of revelation generally will recognise Allah's revelation in the holy Qur-an. An alternative reading is "min 'indi-hi", which is written the same in Arabic, with only three vowel points different. If we adopt that, the last clause will be: "and from Him is (all) knowledge of the Book": i.e., 'as all knowledge of the Book comes from Allah, the Qur-an also bears witness to me'.
Mustafa Khattab Quran Translation
The disbelievers say, “You ˹Muḥammad˺ are no messenger.” Say, ˹O Prophet,˺ “Allah is sufficient as a Witness between me and you, as is whoever has knowledge of the Scripture.”
Piktal Quran Translation
They who disbelieve say: Thou art no messenger (of Allah). Say: Allah, and whosoever hath true knowledge of the Scripture, is sufficient witness between me and you.
Wayaqoolu allatheena kafaroo lasta mursalan qul kafa biAllahi shaheedan baynee wabaynakum waman AAindahu AAilmu alkitabi