Al-Kāfi - Volume 3 > Necessity of Ghusl (bath) on Friday
Hadith #5

5ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ إِبْرَاهِيمَ بْنِ إِسْحَاقَ الأحْمَرِ عَنْ عَبْدِ الله بْنِ حَمَّادٍ الأنْصَارِيِّ عَنْ صَبَّاحٍ الْمُزَنِيِّ عَنِ الْحَارِثِ بْنِ حَصِيرَةَ عَنِ الأصْبَغِ قَالَ كَانَ أَمِيرُ الْمُؤْمِنِينَ (عَلَيْهِ الْسَّلام) إِذَا أَرَادَ أَنْ يُوَبِّخَ الرَّجُلَ يَقُولُ وَالله لأَنْتَ أَعْجَزُ مِنَ التَّارِكِ الْغُسْلَ يَوْمَ الْجُمُعَةِ وَإِنَّهُ لاَ يَزَالُ فِي طُهْرٍ إِلَى الْجُمُعَةِ الأخْرَى.

5. A number of our people have narrated from Ibrahim ibn Ishaq al-Ahmar from ‘Abd Allah ibn Hammad al-Ansariy from Sabbah al- Muzniy from al-Harith ibn Hasirah from al-Asbagh who has said the following: “When ’Amir al-Mu’minin, ‘Alayhi al-Salam, wanted to reprimand a person he (the Imam) would say, ‘By Allah, your failure is greater than one who fails to take Ghusl (bath) on Friday. It certainly is Tahur (cleansing) until next Friday.’”