Skandapurana 5.271.42

5.271.42

brāhmaṇānāṃ tataḥ śūdrā upadeśaṃ vadaṃti ca ..
alpodakāstathā meghā alpasasyā ca medinī .. 42 ..

then śūdras utter instruction to brahmins. / The clouds have little water, and the earth little grain;