One verse

Bhagavad Gita 6.11

6.11

शुचौ देशे प्रतिष्ठाप्य स्थिरमासनमात्मनः | नात्युच्छ्रितं नातिनीचं चैलाजिनकुशोत्तरम् ||६-११||

śucau deśe pratiṣṭhāpya sthiramāsanamātmanaḥ . nātyucchritaṃ nātinīcaṃ cailājinakuśottaram ||6-11||

śucau
in a sanctified
deśe
land
pratiṣṭhāpya
placing
sthiram
firm
āsanam
seat
ātmanaḥ
his own
na
not
ati
too
ucchritam
high
na
nor
ati
too
nīcam
low
caila-ajina
of soft cloth and deerskin
kuśa
and kuśa grass
uttaram
covering

To practice yoga, one should go to a secluded place and should lay kuśa grass on the ground and then cover it with a deerskin and a soft cloth. The seat should be neither too high nor too low and should be situated in a sacred place. The yogī should then sit on it very firmly and practice yoga to purify the heart by controlling his mind, senses and activities and fixing the mind on one point.