Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
malik:20-170 – Yaḥyá > Mālik > Jaʿfar b. Muḥammad from his father

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."  

مالك:٢٠-١٧٠ – وَحَدَّثَنِي يَحْيَى عَنْ مَالِكٍ عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ عَنْ أَبِيهِ

عَنْ عَلِيِّ بْنِ أَبِي طَالِبٍ كَانَ يَقُولُ مَا اسْتَيْسَرَ مِنَ الْهَدْىِ شَاةٌ  

See similar narrations below:

Collected by Bayhaqī
bayhaqi:8896 – Abū Aḥmad al-Mihrajānī al-ʿAdl > Abū Bakr b. Jaʿfar al-Muzakkī > Muḥammad b. Ibrāhīm > Ibn Bukayr > Mālik > Jaʿfar b. Muḥammad from his father > ʿAlī

[Machine] Ali ibn Abi Talib used to say that the least amount of sacrifice that can be made is a sheep.  

البيهقي:٨٨٩٦ – وَأَخْبَرَنَا أَبُو أَحْمَدَ الْمِهْرَجَانِيُّ الْعَدْلُ أنبأ أَبُو بَكْرِ بْنُ جَعْفَرٍ الْمُزَكِّي ثنا مُحَمَّدُ بْنُ إِبْرَاهِيمَ ثنا ابْنُ بُكَيْرٍ ثنا مَالِكٌ عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ عَنْ أَبِيهِ

أَنَّ عَلِيَّ بْنَ أَبِي طَالِبٍ ؓ كَانَ يَقُولُ مَا اسْتَيْسَرَ مِنَ الْهَدْيِ شَاةٌ