I advised my friend to offer qada prayers of his deceased father and to pray for his forgivness as this is compulsory (wajib) on the children. He replied that his father had left him and his mother. He also said that his father didn't fulfill their needs and didn't pay attention to him and his mother. Because of that, he said it is not wajib upon him to pray for his father and offer his qada prayers.
What does Islam say about this?