Hadith about Animal of Aqiqa
The Prophet of Rahmah, the Intercessor of Ummah (May Peace and blessing of ALLAH be upon him) said, if anyone has a child born to him and wishes to offer a sacrifice on its behalf, he may offer two resembling sheep for a boy and one for a girl.
(Sunan Abu Dawood, vol. 3, pp. 143, Hadis 2841)