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SB 10.8.14

prāg ayaṁ vasudevasya
 kvacij jātas tavātmajaḥ
vāsudeva iti śrīmān
 abhijñāḥ sampracakṣate
Synonyms: 
prāk — before; ayam — this child; vasudevasya — of Vasudeva; kvacit — sometimes; jātaḥ — was born; tava — your; ātmajaḥ — Kṛṣṇa, who has taken birth as your child; vāsudevaḥ — therefore He may be given the name Vāsudeva; iti — thus; śrīmān — very beautiful; abhijñāḥ — those who are learned; sampracakṣate — also say that Kṛṣṇa is Vāsudeva.
Translation: 
For many reasons, this beautiful son of yours sometimes appeared previously as the son of Vasudeva. Therefore, those who are learned sometimes call this child Vāsudeva.
Purport: 

Garga Muni indirectly disclosed, “This child was originally born as the son of Vasudeva, although He is acting as your child. Generally He is your child, but sometimes He is the son of Vasudeva.”