Salman bin Amir al-Dabbi (may Allah be pleased with him) says that he heard the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) commanded the aqiqah at a child's birth and said: "Shed blood on his behalf and remove the impurity from him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19260