What is the oldest written source in this country that mentions this right?
Honduras
The first assertion of the right to associate in Honduras was in their Constitution of 1880. The right is located in Chapter Two, Article 9, Number 5 (“Constitución de Honduras de 1880”, 1880).
“Constitución de Honduras de 1880.” 1880. Biblioteca Virtual Miguel de Cervantes. Biblioteca Virtual Miguel de Cervantes. November 1. https://www.cervantesvirtual.com/obra-visor/constitucion-de-honduras-de-1880/html/44ec3699-d923-4453-8da4-3f3ab7f0fe36_2.html#I_0_.