Unwritten laws

such laws as have been handed down by tradition or in song. Such were the laws of the early nations of Europe.

See also: Unwritten

References in classic literature ?
By all the unwritten laws of savage warfare it is always the redskin who attacks, and with the wiliness of his race he does it just before the dawn, at which time he knows the courage of the whites to be at its lowest ebb.
There are written laws -- they perish; but there are also unwritten laws -- THEY are eternal.
Thirteen hundred years hence -- so says the unwritten law -- the
It had its unwritten laws, and they were as clearly defined and as strict as any that could be found among the printed statues of the land.
The Socialists had many branches in America, and the deceased had, no doubt, infringed their unwritten laws, and been tracked down by them.
More than ever was Boris resolved to serve in future not according to the written code, but under this unwritten law.
I recognize your right to make explorations as well as ourselves, and I presume you have not fallen so low that you will not recognize the unwritten law in a case of this kind--the law which says the right of discovery belongs to the one who first makes it.
Now Tarzan felt no fear of Taug, nor did the unwritten law of the jungle demand that he should flee from battle with any male, unless he cared to from purely personal reasons.
He had entered the lists in mortal combat and true to the primitive instincts of the wild--the unwritten law of the jungle--one or both must die before the battle ended.
According to an unwritten law, the buying a drink included the privilege of loafing for just so long; then one had to buy another drink or move on.
With all my experience, I know the unwritten laws of football.
Perhaps this is just one of the unwritten laws of modern political life - part of the process in which our state and our politics develops.