What is the oldest written source in this country that mentions this right?
Ukraine
The first instance of Ukraine allowing the freedom of association is the Ukraine SSR’s 1937 Constitution which entails the (в) свобода зборів і мітингів,г) свобода вуличних походів і демонстрацій.) which translates to the freedom of c) freedom of assembly and rallies, d) freedom of street marches and demonstrations, which can be equivalent to the freedom of association.
Extraordinary XIV Ukrainian Congress of Soviets. 1937. “Constitution (Basic Law) of the Ukrainian Soviet Socialist Republic .” Wikisource. 1937.