Hadith: The Messenger of Allah (may Allah’s peace and blessings be upon him) commanded them to slaughter two similar sheep for a boy and one sheep for a girl (at their birth)

عن عائشة «أن رسول الله صلى الله عليه وسلم أمرهم أن يُعَقَّ عن الغُلَامِ شَاتَانِ مُكَافِئَتَانِ، وعن الْجَارِيَةِ شَاةٌ».
[صحيح] - [رواه الترمذي وأحمد]

‘Ā'ishah (may Allah be pleased with her) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) commanded them to slaughter two similar sheep for a boy and one sheep for a girl (at their birth).
Sahih/Authentic. - [At-Tirmidhi]

Explanation

In this Hadīth, ‘Ā'ishah (may Allah be pleased with her) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) commanded them to slaughter for the ‘Aqīqah of a baby boy two sheep that are similar in age, size, and quality, and to slaughter for the ‘Aqīqah of a baby girl one sheep. ‘Aqīqah is the sacrificial animal slaughtered at the occasion of a baby's birth. It also refers to the banquet where this animal is served.