Al-Kāfi - Volume 3 > Necessity of Ghusl (bath) on Friday
Hadith #7

7ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنْ حَمَّادٍ عَنْ حَرِيزٍ عَنْ بَعْضِ أَصْحَابِنَا عَنْ أَبِي جَعْفَرٍ (عَلَيْهِ الْسَّلام) قَالَ لاَ بُدَّ مِنْ غُسْلِ يَوْمِ الْجُمُعَةِ فِي السَّفَرِ وَالْحَضَرِ فَمَنْ نَسِيَ فَلْيُعِدْ مِنَ الْغَدِ وَرُوِيَ فِيهِ رُخْصَةٌ لِلْعَلِيلِ.

7. Ali ibn Ibrahim has narrated from his father from Hammad from Hariz from certain persons of our people who has said the following: “Abu Ja‘far, ‘Alayhi al-Salam, has said, ‘It is necessary to take Ghusl (bath) on Friday, on a journey or at home. If one forgets it, one must do it again next day.’ It is narrated that one suffering from illness is excused.’”