Jundub b. ‘Abdallāh reported God’s messenger as saying, “Recite the Qur’ān as long as you can concentrate on it, but when your concentration flags give it up.”
Ibn ‘Umar reported the Prophet as saying, “He who studies the Qur’ān is like the owner of tethered camels. If he pays attention to them he keeps hold of them, but if he lets them loose they go away."
Qatādā said that when Anas was asked how the Prophet recited the Qur’ān he replied that he did so prolonging the words. Then he recited “In the name of God, the Compassionate, the Merciful,” prolonging each phrase.
Ibn Mas’ūd reported God’s messenger as saying, “It is wrong for one to say that he has forgotten such and such a verse, for he has been made to forget. Study the Qur’ān, for it is more apt to escape from men’s minds than animals.”
(Bukhārī and Muslim, Muslim adding "which are tethered”.)