Narrated Mujahid from `Abdullah bin `Amr

The Prophet (ﷺ) said (to `Abdullah), "Fast three days a month." `Abdullah 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." `Abdullah 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).