Praise be to Allaah.
Holding the Mus-haf for this reason is contrary to the Sunnah, for several reasons:
1. It prevents a person from placing his right hand over his left when standing.
2. It leads to a lot of unnecessary movements, such as opening the Mus-haf, closing it, and placing it under one's arm.
3. These movements are very distracting to the worshipper.
4. It prevents the worshipper from looking at the place of sujood. Many scholars say that looking at the place of sujood is Sunnah and is better.
5. The one who does that may forget that he is in prayer, unless his heart is properly focused upon his being in prayer, unlike when he is standing in a humble and focused manner with his right hand upon his left, tilting his head towards the place of sujood. In this case he will be more likely to remember that he is praying and that he is behind the imaam.