Narrated Abu Hurairah:
that the Messenger of Allah (ﷺ) said: "Qul Huwa Allahu Ahad is equal to a third of the Qur'an." (ID)
English reference (ID): Vol. 5, Book 42, Hadith 2899 (ID)
Arabic reference (ID): Book 45, Hadith 3145 (ID)