Quran 6:19 from Surah Al-An'aam on Divine Marvels.
قُلۡ أَيُّ شَيۡءٍ أَكۡبَرُ شَهَٰدَةٗۖ قُلِ ٱللَّهُۖ شَهِيدُۢ بَيۡنِي وَبَيۡنَكُمۡۚ وَأُوحِيَ إِلَيَّ هَٰذَا ٱلۡقُرۡءَانُ لِأُنذِرَكُم بِهِۦ وَمَنۢ بَلَغَۚ أَئِنَّكُمۡ لَتَشۡهَدُونَ أَنَّ مَعَ ٱللَّهِ ءَالِهَةً أُخۡرَىٰۚ قُل لَّآ أَشۡهَدُۚ قُلۡ إِنَّمَا هُوَ إِلَٰهٞ وَٰحِدٞ وَإِنَّنِي بَرِيٓءٞ مِّمَّا تُشۡرِكُونَ
English translation: Say What thing (is) greatest (as) a testimony Say Allah (is) Witness between me and between you and has been revealed to me this [the] Quran that I may warn you with it and whoever it reaches Do you truly testify that with Allah (there are) gods other Say Not (do) I testify Say Only He (is) God One and indeed, I am free of what you associate (with Him)
Transliteration: qul ayyu shayin akbaru shahadatan quli al-lahu shahidun bayni wabaynakum wauhiya ilayya hadha al-qur'anu li-undhirakum bihi waman balagha a-innakum latashhaduna anna ma'a al-lahi alihatan ukh'ra qul la ashhadu qul innama huwa ilahun wahidun wa-innani barion mimma tush'rikuna