Amrah (may Allah have mercy on her) narrates from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "Two equal goats are to be slaughtered as aqiqah for a boy, and one goat for a girl." She says that the Messenger of Allah (peace and blessings be upon him) slaughtered two goats on the seventh day as the aqiqah of Sayyiduna Hasan and Sayyiduna Husayn (may Allah be pleased with them both), ordered their heads to be shaved, and said: "Slaughter in his name and say: 'Bismillah wallahu akbar, Allahumma laka wa ilayk, hadhihi aqiqatu fulan' (In the name of Allah, and Allah is the Greatest; O Allah, for You and to You; this is the aqiqah of so-and-so)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19294