Srimad Bhagavatam Canto 05, Chapter 08, Text 29

SB 5.8.29

aho kastam bhrasto ’ham atmavatam anupathad yad-vimukta-samasta-sangasya vivikta-punyaranya-saranasyatmavata atmani sarvesam atmanam bhagavati vasudeve tad-anusravana-manana-sankirtanaradhananusmaranabhiyogenasunya-sakala-yamena kalena samavesitam samahitam kartsnyena manas tat tu punar mamabudhasyaran mrga-sutam anu parisusrava.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In the body of a deer, Bharata Maharaja began to lament: What misfortune! I have fallen from the path of the self-realized. I gave up my real sons, wife and home to advance in spiritual life, and I took shelter in a solitary holy place in the forest. I became self-controlled and self-realized, and I engaged constantly in devotional service — hearing, thinking, chanting, worshiping and remembering the Supreme Personality of Godhead, Vasudeva. I was successful in my attempt, so much so that my mind was always absorbed in devotional service. However, due to my personal foolishness, my mind again became attached — this time to a deer. Now I have obtained the body of a deer and have fallen far from my devotional practices.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Due to his stringent execution of devotional service, Maharaja Bharata could remember the activities of his past life and how he was raised to the spiritual platform. Due to his foolishness, he became attached to an insignificant deer and thus fell down and had to accept the body of a deer. This is significant for every devotee. If we misuse our position and think that we are fully engaged in devotional service and can do whatever we like, we have to suffer like Bharata Maharaja and be condemned to accept the type of body that impairs our devotional service. Only the human form is able to execute devotional service, but if we voluntarily give this up for sense gratification, we certainly have to be punished. This punishment is not exactly like that endured by an ordinary materialistic person. By the grace of the Supreme Lord, a devotee is punished in such a way that his eagerness to attain the lotus feet of Lord Vasudeva is increased. By his intense desire, he returns home in the next lifetime. Devotional service is very completely described here: tad-anusravana-manana-sankirtanaradhananusmaranabhiyogena. The constant hearing and chanting of the glories of the Lord is recommended in Bhagavad-gita: satatam kirtayanto mam yatantas ca drdha-vratah. Those who have taken to Krsna consciousness should be very careful that not a single moment is wasted and that not a single moment is spent without chanting and remembering the Supreme Personality of Godhead and His activities. By His own actions and by the actions of His devotees, Krsna teaches us how to become cautious in devotional service. Through the medium of Bharata Maharaja, Krsna teaches us that we must be careful in the discharge of devotional service. If we want to keep our minds completely fixed without deviation, we must engage them in devotional service full time. As far as the members of the International Society for Krishna Consciousness are concerned, they have sacrificed everything to push on this Krsna consciousness movement. Yet they must take a lesson from the life of Bharata Maharaja to be very cautious and to see that not a single moment is wasted in frivolous talk, sleep or voracious eating. Eating is not prohibited, but if we eat voraciously we shall certainly sleep more than required. Sense gratification ensues, and we may be degraded to a lower life form. In that way our spiritual progress may be checked at least for the time being. The best course is to take the advice of Srila Rupa Gosvami: avyartha-kalatvam. We should see that every moment of our lives is utilized for the rendering of devotional service and nothing else. This is the secure position for one wanting to return home, back to Godhead.
Srimad Bhagavatam Canto 05, Chapter 08, Text 28
Srimad Bhagavatam Canto 05, Chapter 08, Text 30