Srimad Bhagavatam Canto 09, Chapter 07, Text 07

SB 9.7.7

traisankavo hariscandro
yan-nimittam abhud yuddham
 paksinor bahu-varsikam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The son of Trisanku was Hariscandra. Because of Hariscandra there was a quarrel between Visvamitra and Vasistha, who for many years fought one another, having been transformed into birds.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Visvamitra and Vasistha were always inimical. Formerly, Visvamitra was a ksatriya, and by undergoing severe austerities he wanted to become a brahmana, but Vasistha would not agree to accept him. In this way there was always disagreement between the two. Later, however, Vasistha accepted him because of Visvamitra’s quality of forgiveness. Once Hariscandra performed a yajña for which Visvamitra was the priest, but Visvamitra, being angry at Hariscandra, took away all his possessions, claiming them as a contribution of daksina. Vasistha, however, did not like this, and therefore a fight arose between Vasistha and Visvamitra. The fighting became so severe that each of them cursed the other. One of them said, “May you become a bird,” and the other said, “May you become a duck.” Thus both of them became birds and continued fighting for many years because of Hariscandra. We can see that such a great mystic yogi as Saubhari became a victim of sense gratification, and such great sages as Vasistha and Visvamitra became birds. This is the material world. Abrahma-bhuvanal lokah punar avartino ’rjuna. Within this material world, or within this universe, however elevated one may be in material qualities, one must suffer the conditions of birth, death, old age and disease (janma-mrtyu jara-vyadhi). Therefore Krsna says that this material world is simply miserable (duhkhalayam asasvatam). The Bhagavatam says, padam padam yad vipadam: at every step here there is danger. Therefore, because the Krsna consciousness movement provides the opportunity for the human being to get out of this material world simply by chanting the Hare Krsna mantra, this movement is the greatest benediction in human society.
Srimad Bhagavatam Canto 09, Chapter 07, Text 05-06
Srimad Bhagavatam Canto 09, Chapter 07, Text 08