Is it permissible to supplicate for one's unbelieving parents if it is not known whether they embraced Islam or not?

If the parents were originally disbelievers, it is not permissible to seek forgiveness for them unless they embraced Islam, 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.﴾