Al-Kāfi - Volume 3 > Necessity of Ghusl (bath) on Friday
Hadith #6

6ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ مُوسَى عَنْ أُمِّهِ وَأُمِّ أَحْمَدَ بِنْتِ مُوسَى قَالَتَا كُنَّا مَعَ أَبِي الْحَسَنِ (عَلَيْهِ الْسَّلام) بِالْبَادِيَةِ وَنَحْنُ نُرِيدُ بَغْدَادَ فَقَالَ لَنَا يَوْمَ الْخَمِيسِ اغْتَسِلاَ الْيَوْمَ لِغَدٍ يَوْمِ الْجُمُعَةِ فَإِنَّ الْمَاءَ بِهَا غَداً قَلِيلٌ فَاغْتَسَلْنَا يَوْمَ الْخَمِيسِ لِيَوْمِ الْجُمُعَةِ.

6. A number of our people have narrated from Ahmad ibn Muhammad from al-Husayn ibn Musa from his mother, mother of Ahmad daughter of Musa who have said the following: “We were with abu al-Hassan, ‘Alayhi al-Salam, in the desert on our way to Baghdad. He (the Imam) said to us, ‘Today is Thursday, take Ghusl (bath) for Friday, tomorrow water will be scarce.’ We took Ghusl (bath) on Thursday for Friday.’”