Sahih Muslim Book 4, Hadith Number 1720.

Chapter : Concerning dozing off in prayer, or faltering of one’s tongue in the recitation of the Qur’an, or in mentioning of Allah, one should sleep, or stop it till one becomes lively.

‘Aisha reported that the Apostle of Allah (may peace be upon him) heard a person reciting the Qur’an at night. Upon this he said: May Allah show mercy to him; he has reminded me of such and such a verse which I had missed in such and such a surah.