It is narrated from Sayyiduna Abu Rafi' (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) called the adhan in the ears of Sayyiduna Hasan and Sayyiduna Husayn (may Allah be pleased with them both) when they were born, and he also ordered it.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 922