Caitanya-caritāmṛta 4.177
kṛṣṇera pratijñā eka āche pūrva haite ye yaiche bhaje, kṛṣṇa tāre bhaje taiche
[krishnera pratijnaa eka aache poorva haite ye yaiche bhaje, krishna taare bhaje taiche]
Blended reading (Sanskrit + English inline)
kṛṣṇera pratijñā eka āche pūrva haite ye yaiche bhaje, kṛṣṇa tāre bhaje taiche
Lord Kṛṣṇa has a promise from before to reciprocate with His devotees according to the way they worship Him.
My note
Source: vedabase.io