It's from The Jungle Book by Rudyard Kipling.

"NOW this is the law of the jungle, as old and as true as the sky,

And the wolf that shall keep it may prosper, but the wolf that shall break it must die.

As the creeper that girdles the tree trunk, the law runneth forward and back;

For the strength of the pack is the wolf, and the strength of the wolf is the pack.

Wash daily from nose tip to tail tip; drink deeply, but never too deep;

And remember the night is for hunting and forget not the day is for sleep.

The jackal may follow the tiger, but, cub, when thy whiskers are grown,

Remember the wolf is a hunter—go forth and get food of thy own.

Keep peace with the lords of the jungle, the tiger, the panther, the bear;

And trouble not Hathi the Silent, and mock not the boar in his lair.

When pack meets with pack in the jungle, and neither will go from the trail,

Lie down till the leaders have spoken; it may be fair words shall prevail.

When ye fight with a wolf of the pack ye must fight him alone and afar,

Lest others take part in the quarrel and the pack is diminished by war.

The lair of the wolf is his refuge, and where he has made him his home,

Not even the head wolf may enter, not even the council may come.

The lair of the wolf is his refuge, but where he has digged it too plain,

The council shall send him a message, and so he shall change it again.

If ye kill before midnight be silent and wake not the woods with your bay,

Lest ye frighten the deer from the crop and thy brothers go empty away.

Ye may kill for yourselves, and your mates, and your cubs as they need and ye can;

But kill not for pleasure of killing, and seven times never kill man.

If ye plunder his kill from a weaker, devour not all in thy pride,

Pack-right is the right of the meanest; so leave him the head and the hide.

The kill of the pack is the meat of the pack. Ye must eat where it lies;

And no one may carry away of that meat to his lair, or he dies.

The kill of the wolf is the meat of the wolf. He may do what he will,

But, till he is given permission, the pack may not eat of that kill.

Lair right is the right of the mother. From all of her years she may claim

One haunch of each kill for her litter, and none may deny her the same.

Cub right is the right of the yearling. From all of his pack he may claim

Full gorge when the killer has eaten; and none may refuse him the same.

Cave right is the right of the father, to hunt by himself for his own;

He is freed from all calls to the pack. He is judged by the council alone.

Because of his age and his cunning, because of his gripe and his paw,

In all that the law leaveth open the word of the head wolf is law.

Now these are the laws of the jungle, and many and mighty are they;

But the head and the hoof of the law and the haunch and the hump is—Obey!"