Srimad Bhagavatam Canto 10, Chapter 36, Text 17

SB 10.36.17

yasodayah sutam kanyam
 devakyah krsnam eva ca
ramam ca rohini-putram
 vasudevena bibhyata
nyastau sva-mitre nande vai
 yabhyam te purusa hatah
 
Translation: 
 
[Narada told Kamsa:] Yasoda’s child was actually a daughter, and Krsna is the son of Devaki. Also, Rama is the son of Rohini. Out of fear, Vasudeva entrusted Krsna and Balarama to his friend Nanda Maharaja, and it is these two boys who have killed your men.
 
Purport: 
 
Kamsa had been led to believe that Krsna was the son of Yasoda and that Devaki’s eighth child had been a daughter. The identity of Devaki’s eighth child was extremely important to Kamsa because a prophecy had foretold that her eighth child would kill him. Here Narada informs the King that the eighth child of Devaki was the formidable Krsna, thus implying that the prophecy should be taken very seriously. Having received this information, Kamsa obviously will now do everything in his power to kill Krsna and Balarama.
Srimad Bhagavatam Canto 10, Chapter 36, Text 16
Srimad Bhagavatam Canto 10, Chapter 36, Text 18