It is narrated from Sayyidah Umm Kurz al-Khuza'iyyah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: "In the aqiqah, for a boy there are two sheep, and for a girl one sheep."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21861