Marwan al-Asfar said: I saw Ibn Umar make his camel kneel down facing the qiblah, then he sat down urinating in its direction. So I said: AbuAbdurRahman, has this not been forbidden? He replied: Why not, that was forbidden only in open country; but when there is something between you and the qiblah that conceals you , then there is no harm.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى بْنِ فَارِسٍ، حَدَّثَنَا صَفْوَانُ بْنُ عِيسَى، عَنِ الْحَسَنِ بْنِ ذَكْوَانَ، عَنْ مَرْوَانَ الأَصْفَرِ، قَالَ رَأَيْتُ ابْنَ عُمَرَ أَنَاخَ رَاحِلَتَهُ مُسْتَقْبِلَ الْقِبْلَةِ ثُمَّ جَلَسَ يَبُولُ إِلَيْهَا فَقُلْتُ يَا أَبَا عَبْدِ الرَّحْمَنِ أَلَيْسَ قَدْ نُهِيَ عَنْ هَذَا قَالَ بَلَى إِنَّمَا نُهِيَ عَنْ ذَلِكَ فِي الْفَضَاءِ فَإِذَا كَانَ بَيْنَكَ وَبَيْنَ الْقِبْلَةِ شَىْءٌ يَسْتُرُكَ فَلاَ بَأْسَ .
sunnah.com