The Messenger of Allah (ﷺ) came out to us and said: I am going to recite before you one-third of the Qur'an. He (the Holy Prophet) then recited:" Say: He is Allah, One--Allah, the Eternal," to the end of the Surah.
Sahih Muslim Book 6, Hadith 317
← Previous Hadith Get together. 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 Apostle 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 (Surah Ikhlas) is equivalent to one-third of the Qur'an.

Sahih Muslim Book 6, Hadith 316 Next Hadith → The Messenger of Allah (ﷺ) sent a man in charge of an expedition and he would recite for his Companions during their prayer, ending (recitation) with:" Say, He is God, One." When they returned mention was made of it to the Messenger of Allah (ﷺ). He (the Holy Prophet) told them to ask him why he had done like that. So they asked him and he said: Verily, it is an attribute of the Compassionate One, and (for this reason) I love to recite it. The Messenger of Allah (ﷺ) thereupon said: Inform him that Allah loves him.

Sahih Muslim Book 6, Hadith 318