Reference: Fataawa Noor ‘alad-Darb – Question No.6335, Pages 172-173, Volume 12
Question: Is it permissible for a son to supplicate for his father who has died whilst having abandoned the prayer?
Response: It is not permissible for this questioner to supplicate for his father who died whilst having abandoned the prayer. That is because the one who has abandoned the prayer is a disbeliever; according to the preponderant opinion [of the people of knowledge] this disbelief has rendered him out of the fold of Islaam.
[That being the case therefore], it is not permissible for anyone to supplicate for his forgiveness or mercy, as Allaah (Ta’aala) says: