Al-Kāfi - Volume 3 > Necessity of Ghusl (bath) on Friday
Hadith #2

2ـ عَلِيُّ بْنُ مُحَمَّدٍ عَنْ سَهْلِ بْنِ زِيَادٍ وَمُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ أَبِي نَصْرٍ عَنْ مُحَمَّدِ بْنِ عَبْدِ الله قَالَ سَأَلْتُ الرِّضَا (عَلَيْهِ الْسَّلام) عَنْ غُسْلِ يَوْمِ الْجُمُعَةِ فَقَالَ وَاجِبٌ عَلَى كُلِّ ذَكَرٍ وَأُنْثَى عَبْدٍ أَوْ حُرٍّ.

2. Ali ibn Muhammad has narrated from Sahl ibn Ziyad and Muhammad ibn Yahya from Ahmad ibn Muhammad ibn abu Nasr from Muhammad ibn ‘Abd Allah who has said the following: “I once asked al-Rida’, ‘Alayhi al-Salam, about Ghusl (bath) on Friday. He (the Imam) said, ‘It is obligatory on every male, female, slave or free.’”