Yahya related to me from Malik from Jafar ibn Muhammad from his father that Ali ibn Abi Talib used to say, "The least difficult thing acceptable as a sacrificial animal is a sheep."


وَحَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، عَنْ عَلِيِّ بْنِ أَبِي طَالِبٍ، كَانَ يَقُولُ ‏{‏مَا اسْتَيْسَرَ مِنَ الْهَدْىِ‏}‏ شَاةٌ ‏.‏
USC-MSA web (English) reference : Book 20, Hadith 167
Arabic reference : Book 20, Hadith 869