Reference: al-Muntaqaa min Fataawa Shaykh Saalih al-Fowzaan – Volume 2, Page 35, Fatwa No.16
Question: Is the recitation (of the Qur.aan) from the mus.haf better than the recitation by heart? We anticipate you benefit us (with your response).
Response: As from the point of view of reciting the Qur.aan in other than the salaah, then the recitation from the mus.haf is better, as this is more closer to precision and protecting (oneself from error). However, if his recitation via memory is stronger and (affords him) more concentration, then let him read from memory.
As for the salaah, then that which is better is to recite from memory, and that is because if he was to recite from the mus.haf then he will busy himself in holding the mus.haf and putting it (down/to one side when necessary) and in turning over the pages and in following (the recitation) by looking at the words, and likewise he will forgo (the action of) placing his right hand over his left upon his chest whilst he is standing, and quite possibly he will forsake (his concentration) in the rukoo’ and in the sujood if he was to place the mus.haf under his armpits, and because of this we have recommended the recitation of the one praying to be from memory as opposed to reciting from the mus.haf.
Having said this, we notice some of those who are praying behind the imaam holding the mus.haf and following the recitation of the imaam. This is not befitting for that which entails those issues we have (just) mentioned, and (in addition) there is nothing required of them except to follow the imaam. Yes, if we were to assume that the imaam was not strong in his memorisation and he has said to one of those praying behind him: "Pray behind me and follow me (my recitation) in the mus.haf in case I make a mistake" and he (thereby) does so, then there is no harm in this.