Al-Kāfi - Volume 4 > Excellence of Performing Salat (Prayer) in Masjid al-Haram (the Sacred Masjid) and the Best Place Therein
Hadith #5

5ـ أَحْمَدُ بْنُ مُحَمَّدٍ عَنْ عَلِيِّ بْنِ أَبِي سَلَمَةَ عَنْ هَارُونَ بْنِ خَارِجَةَ عَنْ صَامِتٍ عَنْ أَبِي عَبْدِ الله عَنْ آبَائِهِ (عَلَيْهِم السَّلاَم) قَالَ الصَّلاةُ فِي الْمَسْجِدِ الْحَرَامِ تَعْدِلُ مِائَةَ أَلْفِ صَلاةٍ.

5. Ahmad ibn Muhammad has narrated from Ali ibn abu Salmah from Flarun ibn Kharijah from Samet 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.”