CC Madhya 13.160
diṣṭyā yad āsīn mat-sneho
mayi — unto Me; bhaktiḥ — the nine kinds of devotional service, such as śravaṇa, kīrtana and smaraṇa; hi — certainly; bhūtānām — of all living entities; amṛtatvāya — for becoming eternal associates of the Lord; kalpate — is quite befitting; diṣṭyā — by good fortune; yat — whatever; āsīt — there was; mat-snehaḥ — love and affection for Me; bhavatīnām — of all you gopīs; mat-āpanaḥ — the cause for getting Me back.
Lord Śrī Kṛṣṇa said: “Devotional service unto Me is the only way to attain Me. My dear gopīs, whatever love and affection you have attained for Me by good fortune is the only reason for My returning to you.”
This is a verse from Śrīmad-Bhāgavatam (10.82.44).