Is it an act of disbelief to ask for mercy for a disbeliever, and is one not excused by ignorance?

It is not permissible to supplicate for a deceased disbeliever for forgiveness and mercy, based on the words of Allah Almighty: "It is not for the Prophet and those who have believed to ask forgiveness for polytheists, even if they were relatives." (Quran 9:113). If someone commits this forbidden act out of ignorance, they should be informed of Allah's ruling and prohibited from this evil. They are not to be judged as disbelievers or transgressors except after Allah's ruling has been clarified to them and the proof established against them.