The Prophet ﷺ said, "Say, He is Allah, the One, equals, or is equivalent to, a third of the Quran."
حدثنا يحيى عن مالك حدثنا عبد الرحمن بن عبد الله بن عبد الرحمن بن أبي صعصعة عن أبيه
عن النبي ﷺ قال قل هو الله أحد تعدل أو تعدل بثلث القرآن
Its isnad is sahih. Abdul-Rahman bin Abdullah bin Abdul-Rahman bin Abu Sasaa is trustworthy, as is his father, and Malik is Ibn Anas, the famous imam. The hadith was mentioned previously at 11057.