Bhagavad Gita · 6.11

शुचौ देशे प्रतिष्ठाप्य स्थिरमासनमात्मनः।नात्युच्छ्रितं नातिनीचं चैलाजिनकुशोत्तरम्॥

śhuchau deśhe pratiṣhṭhāpya sthiram āsanam ātmanaḥ nāty-uchchhritaṁ nāti-nīchaṁ chailājina-kuśhottaram

In a clean place, having established a firm seat for oneself — neither too high nor too low — covered with kusha grass, deerskin, and cloth, one upon another —

— Bhagavad Gita 6.11

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