Śrīmad-Bhāgavatam 2.1.18

The first process of spiritualizing the mind by mechanical chanting of the praṇava (oṁkāra) and by control of the breathing system is technically called the mystic or yogic process of prāṇāyāma, or fully controlling the breathing air. The ultimate state of this prāṇāyāma system is to be fixed in trance, technically called samādhi. But experience has proven that even the samādhi stage also fails to control the materially absorbed mind. For example, the great mystic Viśvāmitra Muni, even in the stage of samadhi, became a victim of the senses and cohabited with Menakā. History has already recorded this. The mind, although ceasing to think of sensual activities at present, remembers past sensual activities from the subconscious status and thus disturbs one from cent percent engagement in self-realization. Therefore, Śukadeva Gosvāmī recommends the next step of assured policy, namely to fix one's mind in the service of the Personality of Godhead. Lord Śrī Kṛṣṇa, the Supreme Personality of Godhead, also recommends this direct process in the Bhagavad-gītā (BG 6.47, Not yet available in the library. Try the live source.). Thus, the mind being spiritually cleansed, one should at once engage himself in the transcendental loving service of the Lord by the different devotional activities of hearing, chanting, etc. If performed under proper guidance, that is the surest path of progress, even for the disturbed mind.