Srimad Bhagavatam Canto 06, Chapter 04, Text 47

SB 6.4.47

aham evasam evagre
 nanyat kiñcantaram bahih
samjñana-matram avyaktam
 prasuptam iva visvatah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Before the creation of this cosmic manifestation, I alone existed with My specific spiritual potencies. Consciousness was then unmanifested, just as one’s consciousness is unmanifested during the time of sleep.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The word aham indicates a person. As explained in the Vedas, nityo nityanam cetanas cetananam (Katha Upanisad 2.2.13): the Lord is the supreme eternal among innumerable eternals and the supreme living being among the innumerable living beings. The Lord is a person who also has impersonal features. As stated in Srimad-Bhagavatam (1.2.11):
vadanti tat tattva-vidas
 tattvam yaj jñanam advayam
brahmeti paramatmeti
 bhagavan iti sabdyate
“Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramatma or Bhagavan.” Consideration of the Paramatma and impersonal Brahman arose after the creation; before the creation, only the Supreme Personality of Godhead existed. As firmly declared in Bhagavad-gita (18.55), the Lord can be understood only by bhakti-yoga. The ultimate cause, the supreme cause of creation, is the Supreme Personality of Godhead, who can be understood only by bhakti-yoga. He cannot be understood by speculative philosophical research or by meditation, since all such processes came into existence after the material creation. The impersonal and localized conceptions of the Supreme Lord are more or less materially contaminated. The real spiritual process, therefore, is bhakti-yoga. As the Lord says, bhaktya mam abhijanati: “Only by devotional service can I be understood.” Before the creation, the Lord existed as a person, as indicated here by the word aham. When Prajapati Daksa saw Him as a person, who was beautifully dressed and ornamented, he actually experienced the meaning of this word aham through devotional service.
Each person is eternal. Because the Lord says that He existed as a person before the creation (agre) and will also exist after the annihilation, the Lord is a person eternally. Srila Visvanatha Cakravarti Thakura therefore quotes these verses from Srimad-Bhagavatam (10.9.13-14):
na cantar na bahir yasya
 na purvam napi caparam
purvaparam bahis cantar
 jagato yo jagac ca yah
tam matvatmajam avyaktam
 martya-lingam adhoksajam
gopikolukhale damna
 babandha prakrtam yatha
The Personality of Godhead appeared in Vrndavana as the son of mother Yasoda, who bound the Lord with rope just as an ordinary mother binds a material child. There are actually no divisions of external and internal for the form of the Supreme Personality of Godhead (sac-cid-ananda-vigraha), but when He appears in His own form the unintelligent think Him an ordinary person. Avajananti mam mudha manusim tanum asritam: although He comes in His own body, which never changes, mudhas, the unintelligent, think that the impersonal Brahman has assumed a material body to come in the form of a person. Ordinary living beings assume material bodies, but the Supreme Personality of Godhead does not. Since the Supreme Personality of Godhead is the supreme consciousness, it is stated herein that samjñana-matram, the original consciousness, Krsna consciousness, was unmanifested before the creation, although the consciousness of the Supreme Personality of Godhead is the origin of everything. The Lord says in Bhagavad-gita (2.12), “Never was there a time when I did not exist, nor you, nor all these kings; nor in the future shall any of us cease to be.” Thus the Lord’s person is the Absolute Truth in the past, present and future.
In this regard, Madhvacarya quotes two verses from the Matsya Purana:
nana-varno haris tv eko
 bahu-sirsa-bhujo rupat
asil laye tad-anyat tu
 suksma-rupam sriyam vina
asuptah supta iva ca
 militakso ’bhavad dharih
anyatranadarad visnau
 sris ca lineva kathyate
suksmatvena harau sthanal
 linam anyad apisyate
After the annihilation of everything, the Supreme Lord, because of His sac-cid-ananda-vigraha, remains in His original form, but since the other living entities have material bodies, the matter merges into matter, and the subtle form of the spirit soul remains within the body of the Lord. The Lord does not sleep, but the ordinary living entities remain asleep until the next creation. An unintelligent person thinks that the opulence of the Supreme Lord is nonexistent after the annihilation, but that is not a fact. The opulence of the Supreme Personality of Godhead remains as it is in the spiritual world; only in the material world is everything dissolved. Brahma-lina, merging into the Supreme Brahman, is not actual lina, or annihilation, for the subtle form remaining in the Brahman effulgence will return to the material world after the material creation and again assume a material form. This is described as bhutva bhutva praliyate. When the material body is annihilated, the spirit soul remains in a subtle form, which later assumes another material body. This is true for the conditioned souls, but the Supreme Personality of Godhead remains eternally in His original consciousness and spiritual body.
Srimad Bhagavatam Canto 06, Chapter 04, Text 46
Srimad Bhagavatam Canto 06, Chapter 04, Text 48