Al-Kāfi - Volume 4 > Excellence of Performing Salat (Prayer) in Masjid al-Haram (the Sacred Masjid) and the Best Place Therein
Hadith #6

6ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ عَنْ أَبِي عَبْدِ الله عَنْ آبَائِهِ (عَلَيْهِم السَّلاَم) قَالَ الصَّلاةُ فِي الْمَسْجِدِ الْحَرَامِ تَعْدِلُ مِائَةَ أَلْفِ صَلاةٍ.

6. Ali ibn Ibrahim has narrated from his father from al-Nawfaliy from al-Sakuniy who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has narrated from his ancestors, ‘Alayhim al-Salam, who have said that performing Salat (prayer) in Masjid al-Haram is equal to one hundred thousand Salat (prayer) elsewhere.”