Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 21
Narated By N/A : Ibn 'Abbas also reported a tradition from the Prophet (pbuh) conveying the simmilar meaning.
The version of Jarir has the wording: "he did not cover himself while urinating."
The version of Abu Mu'awiyah has the wording: "he did not safeguard himself (from urine)."