 On 21 September 1937 , Muhammadiyah , the conservative Nahdatul Ulama ( NU ) , the merchants ' cooperative Sarekat Islam , and several other Islamic groups – which for the past decade had been feuding – united to form an umbrella group : the Indonesian Islamic Assembly ( Majilis Islam Ala Indonesia , or MIAI ) , based in Surabaya . Fakih served as treasurer . In 1938 he was made the head of the Surabaya branch of the Muhammadiyah , replacing Mas Mansoer . Two years later he began working full @-@ time with the MIAI , having been selected as the head of its secretariat in mid @-@ September 1940 . To take this position , he resigned as head of the Surabaya branch of Muhammadiyah and as a city council member . 
