Sayyiduna Salman bin Amir (may Allah be pleased with him) narrates a marfu' hadith that the Prophet (peace and blessings be upon him) said: "A child is held in pledge for his aqiqah; the impurity is to be removed from him, and on the seventh day blood is to be shed on his behalf."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19292
Abdullah bin Buraydah narrates from his father (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The aqiqah may be performed on the seventh, the fourteenth or the twenty-first day."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19293
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
Ja'far bin Muhammad (may Allah have mercy on him) narrates from his father (may Allah have mercy on him) that the Prophet (peace and blessings be upon him) named Sayyiduna Hasan (may Allah be pleased with him) on the seventh day, and the name of Husayn (may Allah be pleased with him) is also derived from Hasan; between the two of them (may Allah be pleased with them both) there was only the gap of one pregnancy.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19295