Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(161)
Chapter: The ablution for boys (youngsters). When they should perform Ghusl (take a bath) and Tuhur (purification). Their attendance at congregational prayers and their rows in the prayers.
(161)
باب وُضُوءِ الصِّبْيَانِ
Sahih al-Bukhari 858

Narrated Abu Sa`id Al-Khudri:

The Prophet (ﷺ) said, "Ghusl (taking a bath) on Friday is compulsory for every Muslim reaching the age of puberty."

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، قَالَ حَدَّثَنَا سُفْيَانُ، قَالَ حَدَّثَنِي صَفْوَانُ بْنُ سُلَيْمٍ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ الْغُسْلُ يَوْمَ الْجُمُعَةِ وَاجِبٌ عَلَى كُلِّ مُحْتَلِمٍ ‏"‏‏.‏
Reference : Sahih al-Bukhari 858
In-book reference : Book 10, Hadith 249
USC-MSA web (English) reference : Vol. 1, Book 12, Hadith 817
  (deprecated numbering scheme)