Srimad Bhagavatam

References to text SB 11.3.21
SB 11.3.21: Therefore any person who seriously desires real happiness must seek a bona fide spiritual master and take shelter of him by initiation. The qualification of the bona fide guru is that he has realized the conclusions of the scriptures by deliberation and is able to convince others of these conclusions. Such great personalities, who have taken shelter of the Supreme Godhead, leaving aside all material considerations, should be understood to be bona fide spiritual masters.

Text
One should mentally honor the devotee who chants the holy name of Lord Kṛṣṇa, one should offer humble obeisances to the devotee who has undergone spiritual initiation [dīkṣā] and is engaged in worshiping the Deity, and one should associate with and faithfully serve that pure devotee who is advanced in undeviated devotional service and whose heart is completely devoid of the propensity to criticize others.
Nectar of Instruction
NoI 5