Sahih al-Bukhari, Volume 4, Book 56, Hadith 693 (USC-MSA) ⓘ

Narrated Abu Huraira: The Prophet said, "We are the last (to come) but we will be the foremost on the Day of Resurrection, nations were given the Book (i.e. Scripture) before us, and we were given the Holy Book after them. This (i.e. Friday) is the day about which they differed. So the next day (i.e. Saturday) was prescribed for the Jews and the day after it (i.e. Sunday) for the Christians. It is incumbent on every Muslim to wash his head and body on a Day (i.e. Friday) (at least) in every seven days."

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا وُهَيْبٌ، قَالَ حَدَّثَنِي ابْنُ طَاوُسٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ نَحْنُ الآخِرُونَ السَّابِقُونَ يَوْمَ الْقِيَامَةِ، بَيْدَ كُلُّ أُمَّةٍ أُوتُوا الْكِتَابَ مِنْ قَبْلِنَا وَأُوتِينَا مِنْ بَعْدِهِمْ، فَهَذَا الْيَوْمُ الَّذِي اخْتَلَفُوا، فَغَدًا لِلْيَهُودِ وَبَعْدَ غَدٍ لِلنَّصَارَى ‏"‏‏.‏ ‏"‏عَلَى كُلِّ مُسْلِمٍ فِى كُلِّ سَبْعَةِ أَيَّامٍ يَوْمٌ يَغْسِلُ رَأْسَهُ وَجَسَدَهُ‏"‏