CC Madhya 8.92

ei ‘preme’ra anurūpa nā pāre bhajite
ataeva ‘ṛṇī’ haya — kahe bhāgavate
Synonyms: 
ei — this; premera — of love of God; anurūpa — exactly to the proportion; — not; pāre — is able; bhajite — to reciprocate; ataeva — therefore; ṛṇī — debtor; haya — becomes; kahe — is stated; bhāgavate — in Śrīmad-Bhāgavatam.
Translation: 
 ‘In Śrīmad-Bhāgavatam [10.32.22] it is said that Lord Kṛṣṇa cannot proportionately reciprocate devotional service in the mādhurya-rasa; therefore He always remains a debtor to such devotees.