金剛般若經疏論纂要 1.174

1.174

恒河者，從阿耨池東面流出，周四十里，沙細如麪，金沙混流。佛多近此說法，故取為喻。

As for the Ganges River, it flows out from the eastern side of Lake Anavatapta, with a circumference of forty li; its sand is as fine as flour, with golden sand mixed in the flow. The Buddha often preached the Dharma near it; therefore it was taken as a simile.