What is the oldest written source in this country that mentions this right?
Israel
While freedom of association is not explicitly outlined in the Israeli Constitution, the addendum Basic Law: Human Dignity and Liberty of 1992 outlines the fundamental freedoms of life, dignity, and protection afforded to all people (Basic Law: Human Dignity and Liberty, 1992).
"[Basic Law: Human Dignity and Liberty]," [Basic Law: Human Dignity and Liberty] (1992): 150-150