CC Ādi 4.160

atyanta-nigūḍha ei rasera siddhānta
svarūpa-gosāñi mātra jānena ekānta
Synonyms: 
atyanta — extremely; nigūḍha — deep; ei — this; rasera — of mellow; siddhānta — conclusion; svarūpa-gosāñi — Svarūpa Dāmodara Gosvāmī; mātra — only; jānena — knows; ekānta — much.
Translation: 
This conclusion of rasa is extremely deep. Only Svarūpa Dāmodara knows much about it.