It is narrated from Sayyidah Umm Kurz al-Khuza'iyyah (may Allah be pleased with her) that she asked the Messenger of Allah (peace and blessings be upon him) about the aqiqah. He (peace and blessings be upon him) said: "For a boy, two equivalent sheep, and for a girl, one sheep."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21860