From Sahih Bukhari (Hadith 5015):
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's 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
Reference: Bukhari 5015