Thompson v. Wilmot
In Maryland in 1790, Ruth Wilmot exchanged her slave Will for a slave named Harry, who belonged to Thomas A. Thompson. Part of the written agreement was that in addition to the swap, Will would be freed within seven years.
Thompson took Will to Kentucky, and after more than seven years, Will was still a slave. Thompson had reneged on the agreement, so Wilmot sued on Will's behalf for his freedom. The Kentucky lower court ruled in Wilmot's favor and awarded her $691.25 in damages; the money was to go to Will. [Slaves could not file a lawsuit in Kentucky.]
Thompson appealed the case to the higher court [Thompson v Wilmot] and lost his case when the lower court's decision was affirmed in 1809. The case set a standard for contractual agreements for the future emancipation of a slave and allowed the original slave owner to file suit for the emancipation of the slave when the terms of the contractual agreement were not honored.
For more see Fathers of Conscience, by B. D. Jones; "In Kentucky" in The Encyclopedic Digest of Virginia and West Virginia, volume XII [fulltext in Google Books]; and "Thompson versus Wilmot" in the Afro-American Encyclopedia.