قُلْ أَيُّ شَيْءٍ أَكْبَرُ شَهَادَةً ۖ قُلِ اللَّهُ ۖ شَهِيدٌ بَيْنِي وَبَيْنَكُمْ ۚ وَأُوحِيَ إِلَيَّ هَٰذَا الْقُرْآنُ لِأُنذِرَكُم بِهِ
Qul ayyu šayʾin akbaru šahādah, quli Llāhu šahīdun baynī wa-baynkum, wa-ūḥiya ilayya hāḏā l-Qurʾānu li-unḏirakum bih
“Say, "What thing is greatest in testimony?" Say, "Allah is witness between me and you. And this Qur'an was revealed to me that I may warn you thereby..."”
Context:
Invoking Allah as the supreme witness.