Sacrifice (Kitab Al-Dahaya)
Dawud :: Book 15 : Hadith 2828
Narrated Umm Kurz al-Ka'biyyah:
I heard the Apostle of Allah (peace_be_upon_him) say: Two resembling sheep are to be sacrificed for a boy and one for a girl.
AbuDawud said: I heard Ahmad (ibn Hanbal) say: The Arabic word mukafi'atani means equal (in age) or resembling each other.