On observing a fisherman killing fish and selling them, the Buddha explains the consequences of cruelty.
Macchabandha sutta - Fisherman
At one time, the Blessed One was wandering on a walking tour in the Kosala region together with a large saṅgha of bhikkhus.
Then, while traveling along the main road, the Blessed One saw a fisherman killing fish and selling them in a certain spot. Having seen this, he stepped aside from the road and sat down at a prepared seat at the foot of a certain tree. Having sat down, the Blessed One addressed the bhikkhus: "Do you see that fisherman over there killing fish and selling them?"
"Yes, venerable sir."
"What do you think, bhikkhus? Have you ever seen or heard of a fisherman, killing fish and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth?"
"No, venerable sir."
"Good, bhikkhus. I too have neither seen nor heard of a fisherman, killing fish and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth. And why is that? Because he looks on cruelly at the captive fish as they are brought for slaughter. Therefore, he neither travels around by elephant or horse, by chariot or vehicle, nor enjoys wealth or lives off a large accumulation of wealth."
"What do you think, bhikkhus? Have you ever seen or heard of a butcher of cows, killing cows and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth?"
"No, venerable sir."
"Good, bhikkhus. I too have neither seen nor heard of a butcher of cows, killing cows and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth. And why is that? Because, bhikkhus, he looks on cruelly at the captive cows as they are brought for slaughter. Therefore, he neither travels around by elephant or horse, by chariot or vehicle, nor enjoys wealth or lives off a large accumulation of wealth."
What do you think, bhikkhus? Have you ever seen or heard of a butcher of sheep … or a butcher of pigs … or a butcher of poultry … or a butcher of deer, killing deer and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth?"
"No, venerable sir."
"Good, bhikkhus. I too have neither seen nor heard of a butcher of deer, killing deer and selling them, who by that action and livelihood, travels around by elephant or horse, by chariot or vehicle, or enjoys wealth or lives off a large accumulation of wealth. And why is that? Because, bhikkhus, he looks on cruelly at the captive deer as they are brought for slaughter. Therefore, he neither travels around by elephant or horse, by chariot or vehicle, nor enjoys wealth or lives off a large accumulation of wealth.
Bhikkhus, one who looks on cruelly at captive animals as they are brought for slaughter will not travel around by elephant or horse, by chariot or vehicle, or enjoy wealth or live off a large accumulation of wealth. What can be said, then, of one who cruelly regards a human being—someone to be killed and brought for slaughter? This will lead to his harm and suffering for a long time. After the breakup of the body, after death, he will be reborn in a state of loss, in a bad destination, in the lower realms, in hell."