Jami` at-Tirmidhi 2900

Narrated Abu Hurairah:that the Messenger of Allah (ﷺ) said: "Gather and I shall recite to you one third of the Qur'an." He said: "So whoever was to gather did so, then the Messenger of Allah (ﷺ) came out and recited Qul Huwa Allahu Ahad. Then he went back in. Some of them said to each other: "The Messenger of Allah (ﷺ) said: 'I shall recite to you one third of the Qur'an' I thought that this was news from the Heavens." Allah's Prophet (ﷺ) came out and said: "Indeed I said that I would recite to you one third of the Qur'an, and it is indeed equal to one third of the Qur'an