In Robert Graves' translation of Apuleius's The Golden Ass, when Psyche asks Juno for help, Juno says she can't help because of one of the Fabian laws.
What is a Fabian law?
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In "The Golden Ass", the particular quote in question (seen here) is:
Besides, I am forbidden by law - one of the Fabian laws - to harbour any fugitive slave-girl without her owner's consent
The University of Wyoming George William Hopper Law Library has this document on Roman Fabian Laws in their Annotated Justinian Code.
They deal with kidnapping, particularly, with a good deal of treatment on the sale of kidnapped (free) individuals into slavery, and the kidnapping of slaves.
So the articles of particular interest would probably be:
9.20.9: The law is not uncertain that a man who conceals another's slave is subject to an accusation under the Fabian law.
9.20.12: If a man knowingly harbors a fugitive slave together with stolen property, he is subject to an action on theft on account thereof, and the rector of the province will cause such property to be restored to you, with the usual penalty, and if you should file an accusation for the crime of kidnapping, the rector will not hesitate to hear you.