Sunan Ibn Majah 3789
سنن ابن ماجه#3789SahihIt was narrated that Abu Masud Al Ansari said:"The Messenger of Allah(ﷺ) said: "Allahu ahad, Al-Wahidus-Samad [Allah (the) One, the One the Self-Sufficient Master] is equivalent to one third of the Quran
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiSahih
In-book reference: 33:133