俱舍論記 8.154

8.154

「又狹水上至二色竝生」者，此約二像同處破。於一狹水同處同時現兩岸像互見分明，曾無一處見二實色，不應謂此二像俱生。此既竝見，故知非實。

"Furthermore, on narrow water [...] two forms arising side by side": this refutes based on two reflections sharing the same place. On a narrow body of water, in the same place and at the same time, reflections of both banks appear and are distinctly visible to one another; never has one seen two real forms in a single place, so one should not claim that these two reflections arise together. Since they are both seen together, we know they are not real.