The Vedanta Sutras of Badarayana: Second Adhyâya. Third Pâda.: II, 3, 34
The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut [1896]
34. And on account of (the text) teaching its wandering about.
The quality of being an agent has to be attributed to the soul for that reason also, that, in a chapter treating of the soul, the text declares it to wander about in the state of sleep, 'The immortal one goes wherever he likes' (Bri. Up. IV, 3, 12);
and again, 'He moves about, according to his pleasure, within his own body' (Bri. Up. II, 1, 18).