Srimad Bhagavatam Canto 04, Chapter 08, Text 44

SB 4.8.44

pranayamena tri-vrta
pranendriya-mano-malam
sanair vyudasyabhidhyayen
manasa guruna gurum
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
After sitting on your seat, practice the three kinds of breathing exercises, and thus gradually control the life air, the mind and the senses. Completely free yourself from all material contamination, and with great patience begin to meditate on the Supreme Personality of Godhead.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
In this verse the entire yoga system is described in summary, and special stress is given to the breathing exercises for stopping the disturbing mind. The mind, by nature, is always oscillating, for it is very fickle, but the breathing exercise is meant to control it. This process of controlling the mind might have been very possible in those days millions of years ago when Dhruva Maharaja took to it, but at the present moment the mind has to be fixed directly on the lotus feet of the Lord by the chanting process. By chanting the Hare Krsna mantra one immediately concentrates on the sound vibration and thinks of the lotus feet of the Lord, and very quickly one is elevated to the position of samadhi, or trance. If one goes on chanting the holy names of the Lord, which are not different from the Supreme Personality of Godhead, naturally his mind becomes absorbed in thought of the Lord.
 
It is here recommended to Dhruva Maharaja that he meditate on the supreme guru, or supreme spiritual master. The supreme spiritual master is Krsna, who is therefore known as caitya-guru. This refers to the Supersoul, who is sitting in everyone’s heart. He helps from within as stated in Bhagavad-gita, and He sends the spiritual master, who helps from without. The spiritual master is the external manifestation of the caitya-guru, or the spiritual master sitting in everyone’s heart.
 
The process by which we give up our thoughts of material things is called pratyahara, which entails being freed from all material thoughts and engagements. The word abhidhyayet, which is used in this verse, indicates that unless one’s mind is fixed, one cannot meditate. The conclusion, therefore, is that meditation means thinking of the Lord within. Whether one comes to that stage by the astanga-yoga system or by the method recommended in the sastras especially for this present age — to constantly chant the holy name of the Lord — the goal is to meditate on the Supreme Personality of Godhead.
Srimad Bhagavatam Canto 04, Chapter 08, Text 43
Srimad Bhagavatam Canto 04, Chapter 08, Text 45