Shudra Dharma (शूद्रधर्मः)

According to the Bhagavata Purana, a Shudra is to render service to the dvijas (brahmanas, kashtriyas and vaishyas) whose means of livelihood constitute his means of subsistence also. (AITM, Vol.9, P.964)

शूद्रस्य द्विजशुश्रूषा वृत्तिश्च स्वामिनो भवेत् ॥ १५॥

śūdrasya dvijaśuśrūṣā vr̥ttiśca svāmino bhavet ॥ 15॥ (Bh. Pu. Skanda 7, Adhyaya 11, Verse 15).