Musnad Ahmad 30:1994

Abu Ahmad narrated to us, Sufyan narrated to us, from Abu al-Zinad, from Musa ibn Abi Uthman, from his father, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "One should not urinate in water that does not flow, then perform ghusl (full-body ablution) from it."