From Bernard of Clairvaux’s Epistolae (106, sect. 2) – found from a partial quote in ch 9 of Huysman’s En Route:
Believe me from experience – you will find something more in forests than in books. Trees and stones will teach you what you cannot hear from your instructors.
Experto crede: aliquid amplius invenies in silvis, quam in libris. Ligna et lapides docebunt te, quod a magistris audire non possis.
Amplius is one of those Latin words that’s always dreadful to render – here’s the Lewis and Short entry for illustration.