CC Madhya 3.121

prabhura antara mukunda jāne bhāla-mate
bhāvera sadṛśa pada lāgilā gāite
Word for word: 
prabhura — of the Lord; antara — the heart; mukunda — Mukunda; jāne — knows; bhāla-mate — very well; bhāvera — to the ecstatic mood; sadṛśa — suitable; pada — verses; lāgilā gāite — began to sing.
Translation: 
When Mukunda saw the ecstasy of Śrī Caitanya Mahāprabhu, he understood the feelings of the Lord and began to sing many stanzas augmenting the force of the Lord’s ecstasy.