Sahih Bukhari
Ablutions (Wudu)
Volume: 001 / Book Number: 004 / Hadith Number: 154
Narrated Anas bin Malik:
Whenever Allah's Apostle went to answer the call of nature, I along with another boy used to carry a tumbler full of water (for cleaning the private parts) and an 'Anza (spear-headed stuck).