Al-Bukhari recorded from Abu Sa`id that a man heard another man reciting
[قُلْ هُوَ اللَّهُ 
أَحَدٌ ]
(Say: "He is Allah, One.'') and he was repeating over and over. So when 
morning came, the man went to the Prophet and mentioned that to him, and it was 
as though he was belittling it. The Prophet said,
«وَالَّذِي نَفْسِي 
بِيَدِهِ إِنَّهَا لَتَعْدِلُ ثُلُثَ الْقُرْآن»
(By He in Whose Hand is my soul, verily it is equivalent to a third of the 
Qur'an.) Abu Dawud and An-Nasa'i also recorded it. Another Hadith Al-Bukhari 
recorded from Abu Sa`id, may Allah be pleased with him, that the Messenger of 
Allah said to his Companions,
«أَيَعْجِزُ 
أَحَدُكُمْ أَنْ يَقْرَأَ ثُلُثَ الْقُرْآنِ فِي لَيْلَةٍ؟»
(Is one of you not able to recite a third of the Qur'an in a single night) 
This was something that was difficult for them and they said, "Which of us is 
able to do that, O Messenger of Allah'' So he replied,
«اللهُ الْوَاحِدُ 
الصَّمَدُ ثُلُثُ الْقُرْآن»
("Allah is the One, As-Samad'' is a third of the Qur'an.) Al-Bukhari was 
alone in recording this Hadith.