The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
4. And because (the pradhâna), on account of there existing nothing beyond it, stands in no relation; (it cannot be active.)
The three gunas of the Sânkhyas when in a state of equipoise form the pradhâna. Beyond the pradhâna there exists no external principle which could either impel the pradhâna to activity or restrain it from activity. The soul (purusha), as we know, is indifferent, neither moves to--nor restrains from--action. As therefore the pradhâna stands in no relation, it is impossible to see why it should sometimes modify itself into the great principle (mahat) and sometimes not. The activity and non-activity (by turns) of the Lord,
on the other hand, are not contrary to reason, on account of his omniscience and omnipotence, and his being connected with the power of illusion (mâyâ).