From Sahih Bukhari (Hadith 5054):
Narrated `Abdullah bin `Amr:Allah's Messenger (ﷺ) 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 Messenger (ﷺ) said, "Then finish the recitation of the Qur'an in seven days, and do not finish it in less than this period
Reference: Bukhari 5054