Caitanya Caritamrita, Madhya lila 7.148:
Śrī Caitanya Mahāprabhu also advised Vāsudeva to preach about Kṛṣṇa and thus liberate living entities. As a result, Kṛṣṇa would very soon accept him as His devotee.
Purport
... If one wants to be recognized as a devotee by Kṛṣṇa, he should take to preaching work, following the advice of Śrī Caitanya Mahāprabhu. Then one will undoubtedly attain the lotus feet of Śrī Kṛṣṇa Caitanya, Lord Kṛṣṇa Himself, without delay.
