Sahih Bukhari Volume 6, Book 61, Hadith Number 574.

Narrated By ‘Abdullah bin ‘Amr : Allah’s Apostle said to me, “Recite the whole Qur’an in one month’s time.” I said, “But I have power (to do more than that).” Allah’s Apostle said, “Then finish the recitation of the Qur’an in seven days, and do not finish it in less than this period.”