Samurah bin Jundub (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "Every child is held in pledge for his aqiqah, so on the seventh day the aqiqah should be offered on the child's behalf, and his head shaved and he be given a name."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19264