Jerome, Saint. Praefatio Hieronymi in Danielem prophetam in Patrologiae cursus completus. Series Latina (Patrologia Latina) 28.1291-1294

[Letter from Saint Jerome to Paula and Eustochium]
Asserting that he writes for Paula and Eustochium, the church, and posterity, not for other contemporary readers, Jerome discusses scholarly problems with the language of the book of Daniel and its apocryphal passages.
Online at Epistolae (Duplicated) (See also Bibliographia record).