Srimad Bhagavatam Canto 01, Chapter 18, Text 18

SB 1.18.18

suta uvaca
aho vayam janma-bhrto ’dya hasma
vrddhanuvrttyapi viloma-jatah
dauskulyam adhim vidhunoti sighram
mahattamanam abhidhana-yogah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Sri Suta Gosvami said: O God, although we are born in a mixed caste, we are still promoted in birthright simply by serving and following the great who are advanced in knowledge. Even by conversing with such great souls, one can without delay cleanse oneself of all disqualifications resulting from lower births.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Suta Gosvami did not take his birth in a brahmana family. He was born in a family of mixed caste, or an uncultured low family. But because of higher association, like Sri Sukadeva Gosvami and the great rsis of Naimisaranya, certainly the disqualification of inferior birth was washed off. Lord Sri Caitanya Mahaprabhu followed this principle in pursuance of the Vedic usages, and by His transcendental association He elevated many lowborn, or those disqualified by birth or action, to the status of devotional service and established them in the position of acaryas, or authorities. He clearly stated that any man, whatever he may be, whether a brahmana or sudra by birth, or a householder or mendicant in the order of society, if he is conversant with the science of Krsna, he can be accepted as an acarya or guru, a spiritual master.
Suta Gosvami learned the science of Krsna from great rsis and authorities like Sukadeva and Vyasadeva and he was so qualified that even the sages of Naimisaranya eagerly wanted to hear from him the science of Krsna in the form of Srimad-Bhagavatam. So he had the double association of great souls by hearing and preaching. Transcendental science, or the science of Krsna, has to be learned from the authorities, and when one preaches the science, he becomes still more qualified. So Suta Gosvami had both the advantages, and thus undoubtedly he was completely freed from all disqualifications of low birth and mental agonies. This verse definitely proves that Srila Sukadeva Gosvami did not refuse to teach Suta Gosvami about the transcendental science nor did the sages of Naimisaranya refuse to hear lessons from him because of his inferior birth. This means that thousands of years ago there was no bar to learning or preaching the transcendental science because of inferior birth. The rigidity of the so-called caste system in Hindu society became prominent within only one hundred years or so when the number of dvija-bandhus, or disqualified men in the families of higher castes, increased. Lord Sri Caitanya revived the original Vedic system, and He elevated Thakura Haridasa to the position of namacarya, or the authority in preaching the glories of the holy name of the Lord, although His Holiness Srila Haridasa Thakura was pleased to appear in a family of Mohammedans.
Such is the power of pure devotees of the Lord. The Ganges water is accepted as pure, and one can become purified after taking a bath in the waters of the Ganges. But as far as the great devotees of the Lord are concerned, they can purify a degraded soul even by being seen by the lowborn, and what to speak of association. Lord Sri Caitanya Mahaprabhu wanted to purify the whole atmosphere of the polluted world by sending qualified preachers all over the world, and it remains with the Indians to take up this task scientifically and thus do the best kind of humanitarian work. The mental diseases of the present generation are more acute than bodily diseases; it is quite fit and proper to take up the preaching of Srimad-Bhagavatam all over the world without delay. Mahattamanam abhidhana also means dictionary of great devotees, or a book full of the words of great devotees. Such a dictionary of the words of great devotees and those of the Lord are in the Vedas and allied literatures, specifically the Srimad-Bhagavatam.
Srimad Bhagavatam Canto 01, Chapter 18, Text 17
Srimad Bhagavatam Canto 01, Chapter 18, Text 19