SB 3.32.9

kṣmāmbho-’nalānila-viyan-mana-indriyārtha-
 bhūtādibhiḥ parivṛtaṁ pratisañjihīrṣuḥ
avyākṛtaṁ viśati yarhi guṇa-trayātmā
 kālaṁ parākhyam anubhūya paraḥ svayambhūḥ
Synonyms: 
kṣmā — earth; ambhaḥ — water; anala — fire; anila — air; viyat — ether; manaḥ — mind; indriya — the senses; artha — the objects of the senses; bhūta — ego; ādibhiḥ — and so on; parivṛtam — covered by; pratisañjihīrṣuḥ — desiring to dissolve; avyākṛtam — the changeless spiritual sky; viśati — he enters; yarhi — at which time; guṇa-traya-ātmā — consisting of the three modes; kālam — the time; para-ākhyam — two parārdhas; anubhūya — after experiencing; paraḥ — the chief; svayambhūḥ — Lord Brahmā.
Translation: 
After experiencing the inhabitable time of the three modes of material nature, known as two parārdhas, Lord Brahmā closes the material universe, which is covered by layers of earth, water, air, fire, ether, mind, ego, etc., and goes back to Godhead.
Purport: 

The word avyākṛtam is very significant in this verse. The same meaning is stated in Bhagavad-gītā, in the word sanātana. This material world is vyākṛta, or subject to changes, and it finally dissolves. But after the dissolution of this material world, the manifestation of the spiritual world, the sanātana-dhāma, remains. That spiritual sky is called avyākṛta, that which does not change, and there the Supreme Personality of Godhead resides. When, after ruling over the material universe under the influence of the time element, Lord Brahmā desires to dissolve it and enter into the kingdom of God, others then enter with him.