Reference: Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah – Volume 6, Page 445
Question: Is it permissible for a person to urinate whilst standing, keeping in mind that nothing [of the urine] touches his body or his clothes?
Response: There is no harm in urinating whilst standing, expecially if there is a need to do so, so long as the place is covered [from public view] such that no-one can see the ‘awrah (legislated private part) of the urinator in addition that nothing of the sprinkles of the urine touches him (body or clothing) either, for that which has been confirmed on the authority of Hudhayfah (radhi-yAllaahu ‘anhu) that the Prophet (sal-Allaahu ‘alayhi wa sallam):
urinated whilst standing
…the authenticity of this [narration] is agreed upon [by both al-Bukhaaree and Muslim].
[That said] however, it is better to urinate whilst sitting [or crouching] because this is more consistent with the actions of the Prophet (sal-Allaahu ‘alayhi wa sallam) and more protective for the ‘awrah and safer from being afflicted by the sprinkles of the urine.