Abu Dawud Book 2, Hadith Number 1385.
Chapter : In how many days should one complete the recitation of the quran.
Narated By Abdullah ibn Amr ibn al-‘As : Yazid ibn Abdullah said that Abdullah ibn Amr asked the Prophet (PBUH): In how many days should I complete the recitation of the whole Qur’an, Apostle of Allah?
He replied: In one month.
He said: I am more energetic to complete it in a period less than this. He kept on repeating these words and lessening the period until he said: Complete its recitation in seven days.
He again said: I am more energetic to complete it in a period less than this.
The Prophet (PBUH) said: He who finishes the recitation of the Qur’an in less than three days does not understand it.