Shaykh Abdul Azeez ibn Baaz rahimahullaah in his Majmoo` Fataawaa vol. 13 pg. 280 was asked the following question:
Q: Is it permissible to pray on behalf of the deceased those obligatory prayers that he did not pray?
A: The performance of prayer on behalf of the deceased is not permissible, and there is no basis for that, rather that (doing acts for the deceased) is as it pertains to fasting, Hajj, repaying a debt, giving in charity and supplication. As for praying on his behalf, then there is no basis for such.