“What is hateful to you, do not to your fellow”
[Talmud:Shabbath31 a].Why not a more positive statement, like:
“That which is good for you, do to your friend”.
Rabbi Salanter answered: the reason is that some things are good for you but bad foryour friend [From the book: Insights – A Talmudic Treasury by Rabbi Saul Weiss]
It is prohibited to inflict unnecessary pain upon animals and birds.
Furthermore , one is obliged to relieve their pain …….
From the book of Dayan: PToledano: Fountain of Blessings [ Mekor HaBerakha]
Some Nice Tora links: