The Messenger of Allah ﷺ said, "Say, He is Allah, the One" [Ikhlas 112:1] is equal to one third of the Quran.
قال رسول الله ﷺ: {قل هو الله أحد} تعدل ثلث القرآن.
Ibn Majah (3788) narrated it from Hasan bin Ali bin Khallal, who said, "Yazid bin Harun told us, from Jareer bin Hazim, from Qatada, from Anas," and he related it. Its chain of transmission is sahih.