In islamic religion, sins that a person commit are forgiveable only if the person ask for forgiveness.But there is a single sin that will never be forgiven.Allah has no partners, friends or descendants, he is only one.Therefore it is mandatory for every muslim to have the belief of "rawhid" in his/her mind.
Praying five times a day is not enough for to be a Mu'min that is a true believer. Prayers is the second pillar of Islam but a pillar is not strong enough to hold the house it has to be supported by many other rigthteous deeds. Allah First and foremost one should have Al - Birr that is the quality of one who believe in Allah, in Tawhid, that is oneness of Allah. One should not associate Allah with anything whatsoever like son, the dead, ancestors, shrines and any other things. Kiama ( Last Day ) To believe in