9 These dreams suggest another question. I do not at this moment concern myself about the mere creations of fancy, which are formed by the emotions of the uneducated. I speak of visitations in sleep, such as the apparition to Joseph in a dream, in the manner experienced in most cases of the kind. In the same manner, therefore, our own friends also who have departed this life before us sometimes come and appear to us in dreams, and speak to us. For I myself remember that Profuturus, and Privatus, and Servilius, holy men who within my recollection were removed by death from our monastery, spoke to me, and that the events of which they spoke came to pass according to their words.
Or if it be some other higher spirit that assumes their form and visits our minds, I leave this to the all-seeing eye of Him before whom everything from the highest to the lowest is uncovered. If, therefore, the Lord be pleased to speak through reason to your Holiness on all these questions, I beg you to be so kind as make me partaker of the knowledge which you have received. There is another thing which I have resolved not to omit mentioning, for perhaps it bears upon the matter now under investigation:
Source: Letters (New Advent)