法苑珠林 65.11

65.11

又正法念經云。經宿之水。若不細觀恐生細蟲。若不漉治不飲不用。是名細持不殺戒。

Furthermore, the Saddharmasmṛtyupasthāna Sūtra says: “With water left overnight, if one does not inspect it closely, there is fear that fine insects may arise. If it is not strained and purified, do not drink or use it. This is called minutely maintaining the precept against killing.”