Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- It is undesirable (makruh) to pass urine while standing so that no splashes of urine catch one’s clothes.
2- However, one can do it if has no choice but he should make sure that no drops of urine fall on his body or clothes.
With regard to this, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Passing urine while standing has been considered makruh (undesirable) by some scholars simply because doing so may cause urine to splash on our body or clothes.
We should, therefore, avoid it unless we are faced with a situation where we have no other choice; for instance, while using a public washroom, if there is a concern of exposing ourselves to communicable diseases if we were to do so while sitting on the toilet.
Makruh is something considered as undesirable; technically speaking, it refers to actions that we should avoid, and if we avoid it, we will be rewarded for it, while, at the same, there is no punishment if we happened to do it.
Haram, on the other hand, is that which is prohibited and we must avoid, for if we do it, we will incur sin and punishment.
If we happen to pass urine while standing because of certain unavoidable circumstances, we must make sure that urine does not splash on our body or clothes. If it does, we must wash ourselves clean before we are eligible to perform prayer.
For more clarification, Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, adds,
The Sunnah is to answer the call of nature sitting, making oneself close to the ground, because this is more concealing, and makes it less likely that spray from one’s urine will come back on one’s body or clothes, making them dirty. If a person can be sure of avoiding this, then it is permissible to urinate standing up.
Allah Almighty knows best.