Muhammad bin Sirin (may Allah have mercy on him) says that Salman (may Allah be pleased with him) said: "The aqiqah is to be done at the child's birth; shed blood on his behalf and remove the harm from him." Muhammad (may Allah have mercy on him) said: "I wanted to know what removing the impurity means, but no one told me."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19261