Is it permissible to say "may he rest in peace" for a non-believer who died recently?

Seeking mercy for disbelievers is forbidden by text and consensus, based on the Almighty's saying: "It is not for the Prophet and those who have believed to ask forgiveness for polytheists, even if they were relatives, after it has become clear to them that they are companions of Hellfire." And for one who dies upon a religion other than Islam, it is not permissible to seek mercy for them or to ask forgiveness for them, because we judge by what is apparent. As for the fate of the Ahl al-Fatrah (people of the interregnum), it is unknown. The Prophet, peace and blessings be upon him, might have been prevented from seeking forgiveness for his mother for divine reasons, among them so that it would not be understood as generally permissible to seek forgiveness for the Ahl al-Fatrah. Seeking forgiveness is legislated for the people of the call (those who received the message), not for others.