Sayyidah Umm Kurz (may Allah be pleased with her) says that the Messenger of Allah (peace and blessings be upon him) said: "For a boy, two equal goats, and for a girl, one goat, as aqiqah."
Ata says: The meat should be cut into joints, but no bone should be broken; it should be cooked, and at the time of slaughter one should say: 'Bismillah wallahu akbar, hadhihi aqiqatu fulan' (In the name of Allah, and Allah is the Greatest; this is the aqiqah of so-and-so). The meat should be cut into pieces, cooked with water and salt, and distributed among the neighbours.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19287