Srimad Bhagvata Mahapurana: Book 1: Chapter 17: Verses 1-16
Suta said There (on the bank of the Saraswati) the king (Pariksit) saw a Sudra, bearing the insignia of royalty, and with a club in his hand belabouring a cow and a bull as though they had no protector. The bull, who was white as a lotus stalk and stood with difficulty on one leg alone, was seen trembling and urinating as it were with fear while being beaten by the Sudra. As for the cow, who yields materials (in the shape of milk, ghee etc.) useful for religious acts (such as the performance of sacrifices etc.), the king found her most miserable, being kicked by the Sudra and bereft of her calf. Her cheeks were bathed in tears, and she had grown very lean and thin and was hungry. Mounted on his gold-plated car and stringing his bow, he challenged the tyrant in accents deep as the rumbling of a cloud:- "Who are you that are powerful enough to strike the weak so violently in this land protected by me ?" Like an actor on the stage you have put on the garb of a king; but by your action you are a Sudra. By striking harmless creatures in a lonely place and at a time when Sri Krsna has gone far away (ascended to His divine Abode) along with Arjuna (the wielder of the Gandiva bow), you have proved yourself to be an offender and therefore, deserve to be slain.
(Turning to the bull, he went on:) "As for yourself, are you some divinity in the guise of a bull, white as a lotus stalk and moving on one foot only, having lost your other three feet, and thus causing us great sorrow? On this earth, securely guarded by the stout arms of the Paurava kings, tears were never seen to drop from the eyes of creatures other than you. Grieve no more, O bull; let your fear of the Sudra be gone. Weep not, mother; may all be well with you so long as I am here to punish the evil-doer. The good reputation, longevity, fortune and prospects in the other world of that wild king go to the dogs, in whose dominion, 0 virtuous one, the people are indiscriminately oppressed by the impious. To put an end to the suffering of the distressed, this indeed is the foremost duty of kings.Therefore, I shall slay this most wicked fellow, and enemy of living beings that he is. Who is it that amputated your three feet, O bull, a quadruped as you are ? Let there be no afflicted souls like you in the realm of kings who are votaries of Sri Krsna. Tell me, 0 bull, who it was that mutilated innocent and good souls like you, and thus sullied the fair name of the Pandavas (the sons of Praia). May good come to you. He who does evil to an innocent creature must have fear from me on all sides. Pious souls are surely benefited when vile creatures are subdued. I shall certainly cut off the arm, along with the armlet adorning it, of the individual, be he a veritable god, who in his unbridled madness inflicts injury on harmless creatures. It is, indeed, the paramount duty of a monarch to protect those who stick to their own Dharma. Punishing according to the injunctions of the scriptures those other people who in this world have strayed from the path of virtue otherwise than in adversity."