摸着石头过河, “to cross the river by feeling for the stones,” comes from a folk saying. Chen Yun, then vice premier, first proposed it as a working method at a government meeting in April 1950. In 1961 he told the Ministry of Chemical Industry that the work must start from reality and “cross the river by feeling the stones.”
The saying is widely linked to Deng Xiaoping and the reforms after 1978. According to scholars cited by Chinese Wikipedia, Deng himself never used it.