asalamualikum is it allowed to have a quran in your hand and than read from it while in prayer jazakallah

Alhamdu Lillah

Yes, it is allowed to hold a Mus-haf in during your optional prayers (Nafl Salah). It was narrated that Thakwan, a slave of Aysha RAA  used to lead her in prayers while holding his Mus-haf.

Doing the same in the obligatory Salah is risky, thus, disliked, because holding a Mus-haf causes a lot of movements to open it, flip the page, close it,..etc. Moving in the obligatory Salah a lot would invalidate it obviously.