Al-Kāfi - Volume 4 > Al-Akbar and al-Asghar al-Hajj (the Greater and Minor al-Hajj)
Hadith #2

2ـ أَبُو عَلِيٍّ الأَشْعَرِيُّ عَنْ مُحَمَّدِ بْنِ عَبْدِ الْجَبَّارِ عَنْ صَفْوَانَ عَنْ ذَرِيحٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ السَّلاَم) قَالَ الْحَجُّ الأَكْبَرُ يَوْمُ النَّحْرِ.

2. Abu Ali al-Ash’ariy has narrated from Muhammad ibn ‘Abd af-Jabbar from Safwan from Dharih who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that the greater al-Hajj is the day of offering sacrifice.”