The obligation of ghusl on Fridays

عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ: الْغُسْلُ يَوْمَ الْجُمُعَةِ وَاجِبٌ عَلَى كُلِّ مُحْتَلِمٍ ‏.‏  

Hazrat Abu Sa‘id al-Khudri^ra narrated that the Prophet^sa said, “Ghusl [the full ritual bath] on Friday is obligatory upon every person who has reached puberty.”

(Sahih al-Bukhari, Kitab al-adhan, Bab wudu’i s-sibyani wa mata yajibu ‘alayhimu l-ghuslu wa t-tuhuru wa hudurihimi l-jama‘ata wa l-‘idayni wa l-jana’iza wa sufufihim, Hadith 858)