SB 11.21.15

mantrasya ca parijñānaṁ
 karma-śuddhir mad-arpaṇam
dharmaḥ sampadyate ṣaḍbhir
 adharmas tu viparyayaḥ
Synonyms: 
mantrasya — (the purification) of a mantra; ca — and; parijñānam — correct knowledge; karma — of work; śuddhiḥ — the purification; mat-arpaṇam — offering unto Me; dharmaḥ — religiousness; sampadyate — is achieved; ṣaḍbhiḥ — by the six (purification of place, time, substance, the doer, the mantras and the work); adharmaḥ — irreligiosity; tu — but; viparyayaḥ — otherwise.
Translation: 
A mantra is purified when chanted with proper knowledge, and one’s work is purified when offered to Me. Thus by purification of the place, time, substance, doer, mantras and work, one becomes religious, and by negligence of these six items one is considered irreligious.
Purport: 

One receives a mantra from the mouth of a bona fide spiritual master, who instructs the disciple in the method, meaning and ultimate purpose of the mantra. The bona fide spiritual master in this age gives his disciple the mahā-mantra, or holy names of God, Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. One who chants this mantra, considering himself to be the eternal servant of the Lord, gradually learns to chant offenselessly and by such purified chanting quickly achieves the highest perfection of life. The Lord here summarizes His discussion of purity and impurity, which manifest ultimately in religious and irreligious life.