SB 9.2.3
prsadhras tu manoh putro
go-palo guruna krtah
palayam asa ga yatto
ratryam virasana-vratah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Among these sons, Prsadhra, following the order of his spiritual master, was engaged as a protector of cows. He would stand all night with a sword to give the cows protection.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
One who becomes virasana takes the vow to stand all night with a sword to give protection to the cows. Because Prsadhra was engaged in this way, it is to be understood that he had no dynasty. We can further understand from this vow accepted by Prsadhra how essential it is to protect the cows. Some son of a ksatriya would take this vow to protect the cows from ferocious animals, even at night. What then is to be said of sending cows to slaughterhouses? This is the most sinful activity in human society.