He (the Messenger of Allah) said: Allah divided the Qur'an into three parts, and he made:" Say: He, Allah is One." one part out of the (three) parts of the Qur'an.
Sahih Muslim Book 6, Hadith 315
← Previous Hadith Is any one of you incapable of reciting a third of the Qur'an in a night? They (the Companions) asked: How could one recite a third of the Qur'an (in a night)? Upon this he (the Holy Prophet) said: "'Say: He is Allah, One' (Qur'an. cxii) is equivalent to a third of the Qur'an."

Sahih Muslim Book 6, Hadith 314 Next 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