Examples:

• You know, it's an unwritten law.
• Such is the unwritten law of the modern Talmud.
• Well, kinda like you said, it's just a sort of... an unwritten law.
• I mean, it's sort of an unwritten law in this business.
• Millie, sweetheart, it's an unwritten law.
• She had no one, but the unwritten law ordered us to take care of her.
• Well, it's sort of like an unwritten law.
• There is no such thing as the unwritten law.
• It's an unwritten law.
• It's an unwritten law.