Version 1 of Level 1 of SBML was published on 2 March 2001.
The specification can be found at:
Identifier for this specification is: https://identifiers.org/combine.specifications:sbml.level-1.version-1
To cite this document use:
Michael Hucka, Andrew Finney, Herbert Sauro, Hamid Bolouri. (2001). Systems Biology Markup Language (SBML) Level 1: Structures and Facilities for Basic Model Definitions. Retrieved from COMBINE, https://identifiers.org/combine.specifications:sbml.level-1.version-1