Quran 3:81 from Surah Aal-i-Imraan on Divine Marvels.
وَإِذۡ أَخَذَ ٱللَّهُ مِيثَٰقَ ٱلنَّبِيِّـۧنَ لَمَآ ءَاتَيۡتُكُم مِّن كِتَٰبٖ وَحِكۡمَةٖ ثُمَّ جَآءَكُمۡ رَسُولٞ مُّصَدِّقٞ لِّمَا مَعَكُمۡ لَتُؤۡمِنُنَّ بِهِۦ وَلَتَنصُرُنَّهُۥۚ قَالَ ءَأَقۡرَرۡتُمۡ وَأَخَذۡتُمۡ عَلَىٰ ذَٰلِكُمۡ إِصۡرِيۖ قَالُوٓاْ أَقۡرَرۡنَاۚ قَالَ فَٱشۡهَدُواْ وَأَنَا۠ مَعَكُم مِّنَ ٱلشَّٰهِدِينَ
English translation: And when took Allah covenant (of) the Prophets Certainly, whatever I (have) given you of (the) Book and wisdom then comes to you a Messenger confirming that which (is) with you you must believe in him and you must help him He said Do you affirm and take on that (condition) My Covenant They said We affirm He said Then bear witness and I (am) with you among the witnesses
Transliteration: wa-idh akhadha al-lahu mithaqa al-nabiyina lama ataytukum min kitabin wahik'matin thumma jaakum rasulun musaddiqun lima ma'akum latu'minunna bihi walatansurunnahu qala a-aqrartum wa-akhadhtum ala dhalikum is'ri qalu aqrarna qala fa-ish'hadu wa-ana ma'akum mina al-shahidina