It is reported on the authority of Abu Huraira that the Messenger of Allah ﷺ said: 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 Apostle 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.

وَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ، وَيَعْقُوبُ بْنُ إِبْرَاهِيمَ، جَمِيعًا عَنْ يَحْيَى، - قَالَ ابْنُ حَاتِمٍ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، - حَدَّثَنَا يَزِيدُ بْنُ كَيْسَانَ، حَدَّثَنَا أَبُو حَازِمٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ﷺ " احْشِدُوا فَإِنِّي سَأَقْرَأُ عَلَيْكُمْ ثُلُثَ الْقُرْآنِ " . فَحَشَدَ مَنْ حَشَدَ ثُمَّ خَرَجَ نَبِيُّ اللَّهِ ﷺ فَقَرَأَ { قُلْ هُوَ اللَّهُ أَحَدٌ} ثُمَّ دَخَلَ فَقَالَ بَعْضُنَا لِبَعْضٍ إِنِّي أُرَى هَذَا خَبَرٌ جَاءَهُ مِنَ السَّمَاءِ فَذَاكَ الَّذِي أَدْخَلَهُ . ثُمَّ خَرَجَ نَبِيُّ اللَّهِ ﷺ فَقَالَ " إِنِّي قُلْتُ لَكُمْ سَأَقْرَأُ عَلَيْكُمْ ثُلُثَ الْقُرْآنِ أَلاَ إِنَّهَا تَعْدِلُ ثُلُثَ الْقُرْآنِ " .