Narrated Abu Said Al-Khudri
A man heard another man reciting (Surat-Al-Ikhlas) 'Say He is Allah, (the) One.' (112. 1) repeatedly. The next morning he came to Allah's Messenger (ﷺ) and informed him about it as if he thought that it was not enough to recite. On that Allah's Messenger (ﷺ) said, "By Him in Whose Hand my life is, this Surah is equal to one-third of the Qur'an!"
Narrated Abu Sa`id Al-Khudri
The Prophet (ﷺ) said to his companions, "Is it difficult for any of you to recite one third of the Qur'an in one night?" This suggestion was difficult for them so they said, "Who among us has the power to do so, O Allah's Messenger (ﷺ)?" Allah Apostle replied: " Allah (the) One, the Self-Sufficient Master Whom all creatures need.' (Surat Al-Ikhlas 112.1--to the End) is equal to one third of the Qur'an."