SB 3.28.8
sucau dese pratisthapya
vijitasana asanam
tasmin svasti samasina
rju-kayah samabhyaset
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
After controlling one’s mind and sitting postures, one should spread a seat in a secluded and sanctified place, sit there in an easy posture, keeping the body erect, and practice breath control.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Sitting in an easy posture is called svasti samasinah. It is recommended in the yoga scripture that one should put the soles of the feet between the two thighs and ankles and sit straight; that posture will help one to concentrate his mind on the Supreme Personality of Godhead. This very process is also recommended in Bhagavad-gita, Sixth Chapter. It is further suggested that one sit in a secluded, sanctified spot. The seat should consist of deerskin and kusa grass, topped with cotton.