After the surrender of Japan on 15 August 1945 and the proclamation of Indonesian Independence on 17 August 1945, on 24 August 1945, the Japanese forces in Mandailing Natal declared that World War II has ended. Although the Japanese did not mention any references to the proclamation of independence, several people in Mandailing Natal began to spread rumor about the proclamation after the return of a Heiho member from Java. Lubis, as the number one official in Mandailing Natal, decided to form a body to investigate the truth of the rumor on 8 September 1945. Hamzah Lubis was sent by Junjungan Lubis to Bukittinggi to meet M. Syafei and Adinegoro about the truth of the rumor. Ayub Sulaeman, the secretary of Padangsidempuan, received a wire from Adnan Kapau Gani about the proclamation. Hamzah Lubis would return on 12 September 1945, bringing copies of the Constitution of Indonesia, law about the Indonesian National Committee, and the text of the proclamation of Indonesian Independence.