Jami` at-Tirmidhi 2899
جامع الترمذي#2899SahihNarrated Abu Hurairah:that the Messenger of Allah (ﷺ) said: "Qul Huwa Allahu Ahad is equal to a third of the Qur'an
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiIsnaad Hasan
In-book reference: 45:25