Samkhya Karika 63

रूपैः सप्तभिरेव तु बध्नात्यात्मानमात्मना प्रकृतिः ।
सैव च पुरुषार्थं प्रति विमोचयत्येकरूपेण ॥ ६३ ॥

rūpaiḥ saptabhireva tu badhnātyātmānam ātmanā prakṛtiḥ ।
saiva ca puruṣārthaṁ prati vimocayatyekarūpeṇa ॥ 63 ॥

Rūpaiḥ=by forms; saptabhiḥ=seven-fold; eva=alone; tu=indeed; badhnāti=binds; ātmānam=herself; ātmanā=by herself; prakṛtiḥ=Prakriti; sa=she; eva=alone; ca=and; puruṣārthaṁ=for the sake of Purusha; prati=towards; vimocayati=liberates; ekarūpeṇa=by means of one form

Prakriti binds herself by herself by means of the seven forms (seven dispositions of the buddhi). Again, she releases herself for the purpose of Purusha by means of one form (one of eight).