SB 10.47.31

ātmā jñāna-mayaḥ śuddho
 vyatirikto ’guṇānvayaḥ
suṣupti-svapna-jāgradbhir
 māyā-vṛttibhir īyate
Synonyms: 
ātmā — the soul; jñāna-mayaḥ — comprising transcendental knowledge; śuddhaḥ — pure; vyatiriktaḥ — separate; aguṇa-anvayaḥ — uninvolved in the reactions of the material modes; suṣupti — in deep sleep; svapna — ordinary sleep; jāgradbhiḥ — and waking consciousness; māyā — of the material energy; vṛttibhiḥ — by the functions; īyate — is perceived.
Translation: 
Being composed of pure consciousness, or knowledge, the soul is distinct from everything material and is uninvolved in the entanglements of the modes of nature. We can perceive the soul through the three functions of material nature known as wakefulness, sleep and deep sleep.
Purport: 

It is clearly stated here that the soul, ātmā, is constituted of pure knowledge, pure consciousness, and is thus ontologically distinct from the material nature. Śrīla Viśvanātha Cakravartī points out that the word ātmā may also be taken to mean “the Supreme Soul, Lord Kṛṣṇa.” Since the Lord has just explained in the previous verses that all material phenomena are expansions of Himself, the phrase māyā-vṛttibhir īyate indicates that by studying this world deeply we will come to the perception of God. From this point of view also, the gopīs were advised not to lament.