Qur'an 6:19

قُلْ أَىُّ شَىْءٍ أَكْبَرُ شَهَـٰدَةً ۖ قُلِ ٱللَّهُ ۖ شَهِيدٌۢ بَيْنِى وَبَيْنَكُمْ ۚ وَأُوحِىَ إِلَىَّ هَـٰذَا ٱلْقُرْءَانُ لِأُنذِرَكُم بِهِۦ وَمَنۢ بَلَغَ ۚ أَئِنَّكُمْ لَتَشْهَدُونَ أَنَّ مَعَ ٱللَّهِ ءَالِهَةً أُخْرَىٰ ۚ قُل لَّآ أَشْهَدُ ۚ قُلْ إِنَّمَا هُوَ إِلَـٰهٌ وَٰحِدٌ وَإِنَّنِى بَرِىٓءٌ مِّمَّا تُشْرِكُونَ

Say (O Muhammad): What thing is of most weight in testimony? Say: Allah is Witness between me and you. And this Qur'an hath been inspired in me, that I may warn therewith you and whomsoever it may reach. Do ye in sooth bear witness that there are gods beside Allah? Say: I bear no such witness. Say: He is only One Allah. Lo! I am innocent of that which ye associate (with Him).