It is reported on the authority of Abu Hurayrah that the Messenger of Allah (ﷺ) said: Gather, for I am going to recite one-third of the Qur'an before you. And those who could get together gathered there. Then the Messenger of Allah (ﷺ) came out and recited:" Say: He, Allah, is One." He then entered (his house). Some of us said to the others: Perhaps there has been some news from the heaven on account of which he has gone Inside (the house). The Messenger of Allah (ﷺ) again came out and said: I told you that I was going to recite one-third of the Qur'in; keep in mind, this (Sūrah Ikhlāṣ) is equivalent to one-third of the Qur'an. Reference: Sahih Muslim 812a.