Sahih Bukhari
Ablutions (Wudu)
Volume: 001 / Book Number: 004 / Hadith Number: 166
Narrated Muhammad Ibn Ziyad:
I heard Abu Huraira saying as he passed by us while the people were performing ablution from a utensil containing water, "Perform ablution perfectly and thoroughly for Abul-Qasim (the Prophet) said, 'Save your heels from the Hell-fire.' "