Al-Kāfi - Volume 4 > Al-Akbar and al-Asghar al-Hajj (the Greater and Minor al-Hajj)
Hadith #3

3ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ وَعَلِيِّ بْنِ مُحَمَّدٍ الْقَاسَانِيِّ جَمِيعاً عَنِ الْقَاسِمِ بْنِ مُحَمَّدٍ عَنْ سُلَيْمَانَ بْنِ دَاوُدَ الْمِنْقَرِيِّ عَنْ فُضَيْلِ بْنِ عِيَاضٍ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ السَّلاَم) عَنِ الْحَجِّ الأَكْبَرِ فَإِنَّ ابْنَ عَبَّاسٍ كَانَ يَقُولُ يَوْمُ عَرَفَةَ فَقَالَ أَبُو عَبْدِ الله (عَلَيْهِ السَّلاَم) قَالَ أَمِيرُ الْمُؤْمِنِينَ (صلَّى اللهُ عَلَيْهِ وَآلِه) الْحَجُّ الأَكْبَرُ يَوْمُ النَّحْرِ وَيَحْتَجُّ بِقَوْلِهِ عَزَّ وَجَلَّ فَسِيحُوا فِي الأَرْضِ أَرْبَعَةَ أَشْهُرٍ وَهِيَ عِشْرُونَ مِنْ ذِي الْحِجَّةِ وَالْمُحَرَّمُ وَصَفَرٌ وَشَهْرُ رَبِيعٍ الأَوَّلِ وَعَشْرٌ مِنْ رَبِيعٍ الآخِرِ وَلَوْ كَانَ الْحَجُّ الأَكْبَرُ يَوْمَ عَرَفَةَ لَكَانَ أَرْبَعَةَ أَشْهُرٍ وَيَوْماً.

3. Ali ibn Ibrahim has narrated from his father and Ali ibn Muhammad al-Qasaniy all from al-Qasim ibn Muhammad from Sulayman ibn Dawud al-Minqariy from Fudayl ibn ‘Iyad who has said the following: “I once asked abu ‘Abd Allah, about the greater al-Hajj because ibn ‘Abbas used to say, ‘It is the day of ‘Arafah.’ Abu ‘Abd Allah, ‘Alayhi al-Salam, said that ’Amir al-Mu’minin, ‘Alayhi al-Salam, has said, ‘The greater al-Hajj is the day of offering sacrifice and he proved it with the words of Allah, the Most Majestic, the Most Glorious, “You can move in the land during four months.” (9:2 ) This is from the twentieth of the month of Dhu al-Hajj ah through the month of al-Muharram, the month of Safar, the month of Rabi‘ al-Awwal and ten days of the month of Rabi‘ al-Akhir. Were it (greater al-Hajj) to begin with the day of ‘Arafah, it became four months and one day.’”