Sahih Muslim
The Book of Purification (Kitab Al-Taharah)
Book Number: 002 / Hadith Number: 555
Hammam b. Munabbih said: Of the ahadith narrated to us by Abfi Huraira from Muhammad the Messenger of Allah (may peace be upon him) one is this: The Messenger or Allah (may peace be upon him) said: You should not urinate in standing water, that is not flowing, then wash in it.