Al-Kāfi - Volume 4 > Al-Akbar and al-Asghar al-Hajj (the Greater and Minor al-Hajj)
Hadith #1

1ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ مُعَاوِيَةَ بْنِ عَمَّارٍ قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ السَّلاَم) عَنْ يَوْمِ الْحَجِّ الأَكْبَرِ فَقَالَ هُوَ يَوْمُ النَّحْرِ وَالْحَجُّ الأَصْغَرُ الْعُمْرَةُ.

1. Ali ibn Ibrahim has narrated from his father from ibn abu ‘Umayr from Mu‘awiyah ibn ‘Ammar who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about the day of greater al-Hajj. He (the Imam) replied, That is the day of offering sacrifice and minor al-Hajj is al-‘Umrah.’”