Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) performed the aqiqah on behalf of Sayyiduna Hasan and Husayn (may Allah be pleased with them both) with one ram each.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19267