SB 11.17.19

śuśrūṣaṇaṁ dvija-gavāṁ
 devānāṁ cāpy amāyayā
tatra labdhena santoṣaḥ
 śūdra-prakṛtayas tv imāḥ
Synonyms: 
śuśrūṣaṇam — service; dvija — of the brāhmaṇas; gavām — of the cows; devānām — of worshipable personalities such as the demigods and the spiritual master; ca — also; api — indeed; amāyayā — without duplicity; tatra — in such service; labdhena — with that which is obtained; santoṣaḥ — complete satisfaction; śūdra — of the śūdras; prakṛtayaḥ — the natural qualities; tu — indeed; imāḥ — these.
Translation: 
Service without duplicity to the brāhmaṇas, cows, demigods and other worshipable personalities, and complete satisfaction with whatever income is obtained in such service, are the natural qualities of śūdras.
Purport: 

When the entire social order is functioning properly according to Vedic standards, everyone is happy and satisfied. Although the śūdras are to be satisfied with whatever income they obtain through their service, they never lack the necessities of life, because the other orders of society, such as kṣatriyas and vaiśyas, are required to be abundantly generous, and the brāhmaṇas are well known for being the most merciful of all. Therefore, if all social classes obey the Vedic injunctions there will be a new and blissful life for the entire human society under the guidance of Kṛṣṇa consciousness.