I say, and with God's help: Praying for mercy is only permissible for a Muslim; because he is the place of God's mercy, while the disbeliever is the place of His wrath. Allah, the Exalted, said: {And do not pray for any of them who dies ever, nor stand at his grave. Indeed, they have disbelieved in Allah and His Messenger and died while they were defiantly disobedient} [At-Tawbah: 84]. And Allah knows best.