आगमे ब्राह्मे विश्वासटिप्पन्यः

And Smr̥ti-passages say the same.

Authoritative authors also teach in their Smr̥tis that a sitting posture subserves the act of meditation: cp. e.g. Bha. Gītā VI. 11,

Having made a firm seat for one’s self on a pure spot.’ For the same reason the Yogaśāstra teaches different sitting posture, viz. the so-called lotus position and so on.