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SB 10.3.43

tṛtīye ’smin bhave ’haṁ vai
 tenaiva vapuṣātha vām
jāto bhūyas tayor eva
 satyaṁ me vyāhṛtaṁ sati
Synonyms: 
tṛtīye — for the third time; asmin bhave — in this appearance (as Kṛṣṇa); aham — I Myself; vai — indeed; tena — with the same personality; eva — in this way; vapuṣā — by the form; atha — as; vām — of both of you; jātaḥ — born; bhūyaḥ — again; tayoḥ — of both of you; eva — indeed; satyam — take as truth; me — My; vyāhṛtam — words; sati — O supremely chaste.
Translation: 
O supremely chaste mother, I, the same personality, have now appeared of you both as your son for the third time. Take My words as the truth.
Purport: 

The Supreme Personality of Godhead chooses a mother and father from whom to take birth again and again. The Lord took birth originally from Sutapā and Pṛśni, then from Kaśyapa and Aditi, and again from the same father and mother, Vasudeva and Devakī. “In other appearances also,” the Lord said, “I took the form of an ordinary child just to become your son so that we could reciprocate eternal love.” Jīva Gosvāmī has explained this verse in his Kṛṣṇa-sandarbha, Ninety-sixth Chapter, where he notes that in text 37 the Lord says, amunā vapuṣa, meaning “by this same form.” In other words, the Lord told Devakī, “This time I have appeared in My original form as Śrī Kṛṣṇa.” Śrīla Jīva Gosvāmī says that the other forms were partial expansions of the Lord’s original form, but because of the intense love developed by Pṛśni and Sutapā, the Lord appeared from Devakī and Vasudeva in His full opulence as Śrī Kṛṣṇa. In this verse the Lord confirms, “I am the same Supreme Personality of Godhead, but I appear in full opulence as Śrī Kṛṣṇa.” This is the purport of the words tenaiva vapuṣā. When the Lord mentioned the birth of Pṛśnigarbha, He did not say tenaiva vapuṣā, but He assured Devakī that in the third birth the Supreme Personality of Godhead Kṛṣṇa had appeared, not His partial expansion. Pṛśnigarbha and Vāmana were partial expansions of Kṛṣṇa, but in this third birth Kṛṣṇa Himself appeared. This is the explanation given in Śrī Kṛṣṇa-sandarbha by Śrīla Jīva Gosvāmī.