Question: Is it permissible for a person to say about a dead person, “Fulaan [i.e. such and such] is Marhoom [i.e. he has been forgiven or bestowed with mercy] or my father is Marhoom [i.e. he has been forgiven or bestowed with mercy]?”
Answer: The statement Al-Marhoom [i.e. the one forgiven or bestowed with mercy] is not permissible to be uttered about a dead person, rather it is to be said: ‘’Rahimahullaah [may Allaah have mercy upon him]- because the first statement [i.e. al-Marhoom] is information given by the speaker whilst he is not aware of the true state of affairs [of the dead person], rather Allaah is the [only] One who knows about it.
[Fataawaa Al-lajnah Ad-Daa-imah 9/141]