New York laws of 1799, an act for the gradual abolition of slavery, specifying that children born to a slave mother after July 4, 1799 were declared legally free--but not until male children had turned 28, and females 25. Slaves born before that date remained in servitude, although they were redefined as indentured servants.
New York State Archives, NYSA_13036-78_L1799_Ch062
New York State Archives, New York (State). Dept. of State. Bureau of Miscellaneous Records. Enrolled acts of the State Legislature. Series 13036-78, Laws of 1799, Chapter 62.