"...How far off we are here from Catholic teaching we have already seen in the decree of the Vatican Council. We shall see later how, with such theories, added to the other errors already mentioned, the way is opened wide for atheism. Here it is well to note at once that, given this doctrine of experience united with the other doctrine of symbolism, every religion, even that of paganism, must be held to be true. What is to prevent such experiences from being met within every religion? In fact that they are to be found is asserted by not a few.
And with what right will Modernists deny the truth of an experience affirmed by a follower of Islam? With what right can they claim true experiences for Catholics alone? Indeed Modernists do not deny but actually admit, some confusedly, others in the most open manner, that all religions are true..."
PASCENDI DOMINICI GREGIS
ENCYCLICAL OF POPE PIUS X ON THE DOCTRINES OF THE MODERNISTS
http://w2.vatican.va/content/pius-x/en/encyclicals/documents/hf_p-x_enc_19070908_pascendi-dominici-gregis.html