Answered by Shaykh Faraz Rabbani
Question: I would like to know if you can hold the Quran while praying nafl prayers? Is it permissible if you want to read for along time?
Answer: In the Name of Allah, Most Merciful and Compassionate
It is not permitted to carry the Qur'an and look at it while praying--whether an obligatory or supererogatory prayer--in the Hanafi school. [Shurunbulali, Maraqi al-Falah]
Reading from it invalidates the prayer according to the relied upon position. [Ibn Abidin/Haskafi, Radd al-Muhtar `ala al-Durr al-Mukhtar] Rather, the sunna is to recite what you have memorized of the Qur'an--and this is a sure incentive to increase in one's memorization of the Qur'an--and to also spend time reciting the Qur'an outside prayer.
As for praying behind an imam who recites from a copy of the Qur'an (such as in tarawih prayers):
This would not be valid according to the stronger (asahh) position in the Hanafi school, because the stronger position is that the validity of praying behind someone is contingent upon the imam's prayer being valid according to the school of the follower. [Ibn Abidin, Radd al-Muhtar]
However, there is a less strong (muqabil al-asahh) position in the Hanafi school that it is valid to pray behind the imam as long as the prayer of the imam is valid according to the imam's own belief (i.e. if his prayer is valid according to any madhhab). This position is valid to follow, according to leading Hanafi scholars, when there is genuine need.
Thus, if the imam in one's local mosque prays tarawih while reading from the Qur'an or when this has become widespread, one may pray behind him, following this position.
And Allah alone gives success.