Maliks Muwatta Book 2, Hadith Number 114.
Section : Urinating Standing and Otherwise.
Yahya related to me from Malik that Abdullah ibn Dinar said, “I saw Abdullah ibn Umar urinating while standing.”
Yahya said that Malik was asked if any hadith had come down about washing the private parts of urine and faeces and he said, “I have heard that some of those who have passed away used to wash themselves of faeces. I like to wash my private parts of urine.”