Custom as source of law
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Custom ("long use") does not confer the authority of law, but (only) the will of the sovereign.
When long use obtaineth the authority of a law, it is not the length of time that maketh the authority, but the will of the sovereign signified by his silence (for silence is sometimes an signified by his silence (for silence is sometimes an argument of consent); and it is no longer law, than the sovereign shall be silent therein. And therefore if the sovereign shall have a question of right grounded, not upon his present will, but upon the laws formerly made, the length of time shall bring no prejudice to his right: but the question shall be judged by equity. For many unjust actions and unjust sentences go uncontrolled a longer time than any man can remember. And our lawyers account no customs law but such as reasonable, and that evil customs are to be abolished: but the judgement of what is reasonable, and of what is to be abolished, belonged to him that maketh the law, which is the sovereign assembly or monarch.
Hobbes, Lev XXVI 7
The diverse customs indigenous to various provinces are regarded as law not due to length of time but due to the sovereign’s authority, and if unwritten, the custom is "no other but a law of nature."
If the Soveraign of one Common-wealth, subdue a people that have lived under other written Lawes, and afterwards govern them by the same Lawes, by which they were governed before; yet those Lawes are the Civill Lawes of the Victor, and not of the Vanquished Common-wealth, For the legislator is he, not by whose authority the laws were first made, but by whose authority they now continue to be laws. And therefore where there be diverse provinces within the dominion of a Commonwealth, and in those provinces diversity of laws, which commonly are called the customs of each several province, we are not to understand that such customs have their force only from length of time; but that they were anciently laws written, or otherwise made known, for the constitutions and statutes of their sovereigns; and are now laws, not by virtue of the prescription of time, but by the constitutions of their present sovereigns. But if an unwritten law, in all the provinces of a dominion, shall be generally observed, and no iniquity appear in the use thereof, that law can be no other but a law of nature, equally obliging all mankind.
Hobbes, Lev XXVI 9