Vaishnava Samhita. Chaturbhujadasa Charitam. Vol III Book VII Chp 12 Shlokas 5 - 6

जन्मान्तरे विष्णुपूजां विधाय भरतो यथा |

योगभ्रष्टा ये भवन्ति जन्मना तेपि वैष्णवाः ||

यदि जन्मान्तरे पुन्यमनन्तञ्चेश्वरार्पितम् |

तदैव प्राप्यते मर्त्यैर्वैष्णवत्वं सुदुर्लभम् ||

Those who are born as yogabhrastas, reaching high levels of spiritual attainment, like Jatabharata due to their devoted service to Lord Vishnu in the previous birth, remain vaishnavas from birth. In the present birth, one attains the unattainable 'vaishnava janma', if he had collected innumerable merits in the previous births with an idea of making them offerings to God.