She is asking about the validity of a du’aa’ to save oneself from the torment of the grave
Question

                Please let me know if this is an authentic dua, if it is then i am missing out on doing it everyday, and if it isn't i would like to know of a dua i can say in its place, please let me know, it is important to me.  The dua is to say durood sharif 3x then say la ilaha illahlahul malikul haqqal mubeen, then say durood sharif 3x again.  I was told that if this is said everyday then one is saved from the tortures of the grave, one will be prosperous in halal earnings, also the person can enter any door in jannah.  Please let me know if this is authentic or not?
Praise be to Allah.
    This du’aa’ is not correct. The way to protect oneself from 
    the torment of the grave is to fear Allaah by doing that which He commands 
    and avoiding that which He has forbidden, and to remember Allaah regularly 
    and read Qur’aan, especially Soorat al-Mulk, as it is proven that this will 
    save one from the torment of the grave, by Allaah’s leave.