Al-Kāfi - Volume 3 > Sprucing up on Fridays
Hadith #2

2ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ مُحَمَّدِ بْنِ الْحُصَيْنِ عَنْ عُمَرَ الْجُرْجَانِيِّ عَنْ مُحَمَّدِ بْنِ الْعَلاَءِ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ سَمِعْتُهُ يَقُولُ مَنْ أَخَذَ مِنْ شَارِبِهِ وَقَلَّمَ مِنْ أَظْفَارِهِ يَوْمَ الْجُمُعَةِ ثُمَّ قَالَ بِسْمِ الله عَلَى سُنَّةِ مُحَمَّدٍ وَآلِ مُحَمَّدٍ كَتَبَ الله لَهُ بِكُلِّ شَعْرَةٍ وَكُلِّ قُلاَمَةٍ عِتْقَ رَقَبَةٍ وَلَمْ يَمْرَضْ مَرَضاً يُصِيبُهُ إِلاَّ مَرَضَ الْمَوْتِ.

2. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from Muhammad ibn al-Husayn from ‘Umar al-Jurjaniy from Muhammad ibn al-‘Ala’ who has said the following: “I heard abu ‘Abd Allah, ‘Alayhi al-Salam, say, ‘One may, on Friday trim his mustache and fingernails. In so doing if one says, “(I do this) in the name of Allah and because of the Sunnah (traditions) of the Holy Prophet, Muhammad, and his family,” Allah writes for him for every hair and piece of fingernail a reward equal to freeing a slave. He will not become ill to a harmful degree except the illness that causes his death.’”