I found this quote below in a SSPX pamphlet. I looked it up to find some context and can't find the full quote because the sermon is just a paraphrased summary. Is there a recording somewhere of the full sermon?
"We believed that after the Council would come a day of sunshine in the history of the Church. But instead there has come a day of clouds and storms, and of darkness.... How did this come about? We will confide to you the thought that may be, we ourselves admit in free discussion, that may be unfounded, and that is that there has been a power, an adversary power. Let us call him by his name: the devil. It is as if from some mysterious crack, no, it is not mysterious, from some crack the smoke of Satan has entered the temple of God." Pope Paul VI Sermon on June 29, 1972