St. Paisios the Athonite, Epistles

 "Geronda, if thoughts are of the type that are not to be spoken, what shall I do?"

He replied:

"I understand which thoughts you mean - those which have to do with God, the divine etc., and many times even about your spiritual Father. All of these thoughts, the blasphemous ones, are from the devil. Blashemies are from the devil, as are all such sins. Therefore, Brother, it is not right to feel upset about the sins of the devil. When someone says to his spiritual Father: 'blasphemous thoughts about God, Christ, the Holy Spirit, the Virgin Mary, the Saints or about you, my spiritual Father, cross my mind' he does not need to say anything further. Neither will the spiritual Father ask for details, nor should we tell him. It suffices to say 'blasphemous thoughts cross my mind'".

"The malefactor devil, so as to ensnare us, brings us thoughts even about the All Holy Spirit and then tells us that this sin is not forgiven, etc. Why is he telling us this? We aleady know that. Let him who blasphemes the Holy Spirit bear it in mind, not us who venerate Him. From this, we are able to see that it is from the devil, since he usually conveys this type of thought to the very devout and sensitive. If he does not manage to bring the man to despair and make him commit suicide, he will at least drive him insane. If he is not able to achieve this either, it pleases hm just to make him despondent. It's enough for the devil if he rener a creature of God useles.."

St. Paisios the Athonite, Epistles