Bhagavad Gita · 6.10

योगी युञ्जीत सततमात्मानं रहसि स्थितः।एकाकी यतचित्तात्मा निराशीरपरिग्रहः॥

yogī yuñjīta satatam ātmānaṁ rahasi sthitaḥ ekākī yata-chittātmā nirāśhīr aparigrahaḥ

The yogi should constantly engage the mind in meditation, sitting in a secluded place, alone, with controlled mind and body, free from expectations and possessiveness.

— Bhagavad Gita 6.10

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