As a sleeping person acts according to the body manifested in his dreams and accepts it to be himself, so one identifies with his present body, which he acquired because of his past religious or irreligious actions, and is unable to know his past or future lives.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यथाज्ञस्तमसा युक्त उपास्ते व्यक्तमेव हि । न वेद पूर्वमपरं नष्टजन्मस्मृतिस्तथा
yathājñastamasā yukta upāste vyaktameva hi | na veda pūrvamaparaṃ naṣṭajanmasmṛtistathā
SB 6.1.49