Sahih al-Bukhari 226

It is related that Abu Wa'il said, "Abu Musa al-Ash'ari used to lay great stress on the question of urinating and said, 'If one of the Banu Isra'il got urine on his garment, he would cut that part out.'" Hudhayfa said, "I wish he had not laid such great stress on this matter. The Messenger of Allah, may Allah bless him and grant him peace, went to the rubbish dump of a people and urinated while standing."* [* The Messenger of Allah, may Allah bless him and grant him peace, used to urinate while sitting. 'A'isha said that the Prophet never urinated while standing, but the Prophet did it to show that it is permissible. 'Umar, 'Ali and Zayd ibn Thabit and other Companions have urinated while standing. Only one must be careful that it did not get on the clothes or body. See Fath al-Bari, I, 330.]