Musnad Ahmad 1268:4

Hajjaj narrated to us, from Ibn Jurayj, and Abd al-Razzaq said: Ibn Jurayj informed us, saying: Ata’ informed me, from Habibah bint Maysarah ibn Abi Khuthaym, from the mother of the children of Karz al-Ka’biyyah, that she asked the Messenger of Allah (peace and blessings of Allah be upon him) about the *aqiqah*. He said: "For the boy, two equivalent sheep, and for the girl, one sheep." I said to Ata’: "What is meant by 'equivalent'?" He said: "The two equals." Hajjaj said in his narration: "And the sheep (rams) are more beloved to me than the goats." And he mentioned that they are more beloved to me than their females. He said: "And we like that its blackness be from it."