Srimad Bhagavatam Canto 10, Chapter 13, Text 19

SB 10.13.19

yavad vatsapa-vatsakalpaka-vapur yavat karanghry-adikam
yavad yasti-visana-venu-dala-sig yavad vibhusambaram
yavac chila-gunabhidhakrti-vayo yavad viharadikam
sarvam visnumayam giro ’nga-vad ajah sarva-svarupo babhau
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
By His Vasudeva feature, Krsna simultaneously expanded Himself into the exact number of missing cowherd boys and calves, with their exact bodily features, their particular types of hands, legs and other limbs, their sticks, bugles and flutes, their lunch bags, their particular types of dress and ornaments placed in various ways, their names, ages and forms, and their special activities and characteristics. By expanding Himself in this way, beautiful Krsna proved the statement samagra-jagad visnumayam: “Lord Visnu is all-pervading.”
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
As stated in the Brahma-samhita (5.33):
advaitam acyutam anadim ananta-rupam
adyam purana-purusam nava-yauvanam ca
Krsna, param brahma, the Supreme Personality of Godhead, is adyam, the beginning of everything; He is adi-purusam, the ever-youthful original person. He can expand Himself in more forms than one can imagine, yet He does not fall down from His original form as Krsna; therefore He is called Acyuta. This is the Supreme Personality of Godhead. Sarvam visnumayam jagat. Sarvam khalv idam brahma. Krsna thus proved that He is everything, that He can become everything, but that still He is personally different from everything (mat-sthani sarva-bhutani na caham tesv avasthitah). This is Krsna, who is understood by acintya-bhedabheda-tattva philosophy. Purnasya purnam adaya purnam evavasisyate: Krsna is always complete, and although He can create millions of universes, all of them full in all opulences, He remains as opulent as ever, without any change (advaitam). This is explained by different Vaisnava acaryas through philosophies such as visuddhadvaita, visistadvaita and dvaitadvaita. Therefore one must learn about Krsna from the acaryas. Acaryavan puruso veda: one who follows the path of the acaryas knows things as they are. Such a person can know Krsna as He is, at least to some extent, and as soon as one understands Krsna (janma karma ca me divyam evam yo vetti tattvatah), one is liberated from material bondage (tyaktva deham punar janma naiti mam eti so ’rjuna).
Srimad Bhagavatam Canto 10, Chapter 13, Text 18
Srimad Bhagavatam Canto 10, Chapter 13, Text 20