What is the origin of the saying "The Yellow River is full of disasters, but only one episode is rich" and "Ningxia is in Huang Hefu"?

After the Han Dynasty, the disaster situation in the lower reaches of the Yellow River became increasingly serious, which brought great disasters to the people in the lower reaches. The Hetao area, however, did not suffer any losses, but gained the benefits of irrigation and became the granary of Saibei. Therefore, there is a saying in history that "the Yellow River is harmful, only one is rich" and "Huang Hefu and Ningxia are the best in the world".