Al-Kāfi - Volume 8 > Hadith
Hadith #161

مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ مَرْوَكِ بْنِ عُبَيْدٍ عَنْ رِفَاعَةَ عَنْ أَبِي عَبْدِ اللَّهِ (عليه السلام) قَالَ قَالَ أَ تَدْرِي يَا رِفَاعَةُ لِمَ سُمِّيَ الْمُؤْمِنُ مُؤْمِناً قَالَ قُلْتُ لَا أَدْرِي قَالَ لِأَنَّهُ يُؤْمِنُ عَلَى اللَّهِ عَزَّ وَ جَلَّ فَيُجِيزُ [اللَّهُ] لَهُ أَمَانَهُ.

161. Muhammad Bin Yahya, from Ahmad Bin Muhammad, from Marouk Bin Ubeyd, from Rafa’at, who has narrated the following: Abu Abdullah (asws) having said: ‘Do you know, O Rafa’at, why the ‘الْمُؤْمِنُ’ Believer is called ‘Momin’?’ I said, ‘I do not know’. He (asws) said: ‘Because he entrusts himself to Allah (azwj) Mighty and Majestic, so Allah (azwj) Authorises safety for him’.