Sahih Muslim 269

Avoid the two things that provoke curse from people, for the one who does any of them is usually abused and reviled by others. These two things are: relieving oneself on the pathways used by people or in the shade, where they take shelter. A similar meaning occurs in the verse that reads: {And do not abuse those they invoke other than Allah, lest they abuse Allah in enmity without knowledge} [Sūrat al-An‘ām: 108].

In other words: Do not cause them to abuse Allah, the Almighty, by abusing their gods. Similarly, the Prophet (may Allah's peace and blessings be upon him) prohibited that a man should abuse his father and mother.

Thereupon, the Companions asked: “Would anyone abuse his own parents?” He said: “Yes. He abuses someone else’s father and that person retaliates by abusing his father and mother.” So it is as if he himself has cursed his own parents, because he was the reason behind it. “The one who relieves himself on people’s roads;” meaning: he urinates or defecates in the places where people walk and pass through.

This is undoubtedly prohibited, regardless of whether it is done by a resident or a traveler, as it causes harm to the people. In the Qur'an, Allah, the Almighty, says: {And those who harm believing men and believing women for [something] other than what they have earned have certainly born upon themselves a slander and manifest sin} [Sūrat al-Ahzāb: 58].

If, however, a person relieves himself on a road not frequented by people, there is nothing wrong with that, given the lack of harm. “Or in their shade;” meaning: he relieves himself in the shade, where people take shelter and rest. There is nothing wrong, however, if one answers the call of nature in the shade in empty places that are not used or frequented by people, given the lack of harm.

The Messenger (may Allah’s peace and blessings be upon him) would sometimes relieve himself in the shade of a host of palm trees.