The Prophet ﷺ said (to ʿAbdullah), "Fast three days a month." ʿAbdullah said, (to the Prophet) "I am able to fast more than that." They kept on arguing on this matter till the Prophet ﷺ said, "Fast on alternate days, and recite the whole Qur'an once a month." ʿAbdullah said, "I can recite more (in a month)," and the argument went on till the Prophet ﷺ said, "Recite the Qur'an once each three days." (i.e. you must not recite the whole Qur'an in less than three days).  

عَنِ النَّبِيِّ ﷺ قَالَ صُمْ مِنَ الشَّهْرِ ثَلاَثَةَ أَيَّامٍ قَالَ أُطِيقُ أَكْثَرَ مِنْ ذَلِكَ فَمَا زَالَ حَتَّى قَالَ صُمْ يَوْمًا وَأَفْطِرْ يَوْمًا فَقَالَ اقْرَإِ الْقُرْآنَ فِي شَهْرٍ قَالَ إِنِّي أُطِيقُ أَكْثَرَ فَمَا زَالَ حَتَّى قَالَ فِي ثَلاَثٍ