CC Antya 19.18

tarajā-prahelī ācārya kahena ṭhāre-ṭhore
prabhu mātra bujhena, keha bujhite nā pāre
Word for word: 
tarajā-prahelī — a sonnet in equivocal language; ācārya — Advaita Ācārya; kahena — spoke; ṭhāre-ṭhore — making some indications; prabhu — Śrī Caitanya Mahāprabhu; mātra — only; bujhena — could understand; keha bujhite nā pāre — others could not understand.
Translation: 
Advaita Ācārya had written a sonnet in equivocal language with an import that Śrī Caitanya Mahāprabhu could understand but others could not.