مُوَطَّأُ مَالِكٍ
Muwatta Malik 871
Hajj
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ {مَا اسْتَيْسَرَ مِنَ الْهَدْى} بَدَنَةٌ أَوْ بَقَرَةٌ .
Yahya related to me from Malik from Nafi that Abdullah ibn Urnar used to say, "The least thing that is acceptable as a sacrificial animal is a camel or a cow."
Arabic/English book reference: Book 20, Hadith 169