I read a story about the Butcher's son which goes like this:
There once was a man who was a srota- aapanna born into the family of a butcher. He was on the threshhold of adulthood. Although he was expected to pursue his household occupation, he was unable to kill animals. His father and mother gave him a knife and a sheep and shut him up in a room, telling him, "If you do not kill the sheep, we will not allow you to come out and see the sun or the moon or to have the food and drink to survive."
The son thought to himself, "If I kill this sheep, then I will[be compelled to] pursue this occupation my entire life. How could I commit this great crime [simply] for the sake of this body?" Then he took up the knife and killed himself. The father and mother opened the door to look. The sheep was standing to one side whereas the son was [laying there], already expired.
At that time, when he killed himself, he was born in the heavens. If one is like this, then this amounts to not sparing [even one's own] life in safeguarding [the integrity of] the pure precepts.
End Notes: A srota-aapanna is a first- stage arhat, otherwise known as a "stream-winner."
If killing is prohibited in all forms, how come the butcher son was born into the heavens? Although his motivation is pure, that he wishes not to pursue a life killing animals, however, taking his own life is also considered killing and karma is formed regardless.