Bhagavad Gita · 18.44

कृषिगौरक्ष्यवाणिज्यं वैश्यकर्म स्वभावजम्।परिचर्यात्मकं कर्म शूद्रस्यापि स्वभावजम्॥

kṛiṣhi-gau-rakṣhya-vāṇijyaṁ vaiśhya-karma svabhāva-jam paricharyātmakaṁ karma śhūdrasyāpi svabhāva-jam

Agriculture, cow protection, and trade are the natural duties of a Vaishya. Service is the natural duty of a Shudra.

— Bhagavad Gita 18.44

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)