The Magna Carta, Article 20:

A freeman shall only be amerced for a small offence according to the measure of that offence. And for a great offence he shall be amerced according to the magnitude of the offence, saving his contenement; and a merchant, in the same way, saving his merchandize. And a villein, in the same way, if he fall under our mercy, shall be amerced saving his wainnage. And none of the aforesaid fines shall be imposed save upon oath of upright men from the neighbourhood.

[The Magna Carta, Article 20]