Narrated Abdullah ibn Amr ibn al-'As:

Yazid ibn Abdullah said that Abdullah ibn Amr asked the Prophet (ﷺ): In how many days should I complete the recitation of the whole Qur'an, Messenger 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 (ﷺ) said: He who finishes the recitation of the Qur'an in less than three days does not understand it.

حَدَّثَنَا ابْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الصَّمَدِ، أَخْبَرَنَا هَمَّامٌ، أَخْبَرَنَا قَتَادَةُ، عَنْ يَزِيدَ بْنِ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، أَنَّهُ قَالَ يَا رَسُولَ اللَّهِ فِي كَمْ أَقْرَأُ الْقُرْآنَ قَالَ ‏"‏ فِي شَهْرٍ ‏"‏ ‏.‏ قَالَ إِنِّي أَقْوَى مِنْ ذَلِكَ - يُرَدِّدُ الْكَلاَمَ أَبُو مُوسَى - وَتَنَاقَصَهُ حَتَّى قَالَ ‏"‏ اقْرَأْهُ فِي سَبْعٍ ‏"‏ ‏.‏ قَالَ إِنِّي أَقْوَى مِنْ ذَلِكَ ‏.‏ قَالَ ‏"‏ لاَ يَفْقَهُ مَنْ قَرَأَهُ فِي أَقَلَّ مِنْ ثَلاَثٍ ‏"‏ ‏.‏