It was narrated from Thawban that:
The Messenger of Allah said: "No one among the Muslims should stand to pray when he is suppressing (the need to urinate or defecate), until he has to relieve himself."

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُصَفَّى الْحِمْصِيُّ، حَدَّثَنَا بَقِيَّةُ، عَنْ حَبِيبِ بْنِ صَالِحٍ، عَنْ أَبِي حَىٍّ الْمُؤَذِّنِ، عَنْ ثَوْبَانَ، عَنْ رَسُولِ اللَّهِ ـ ﷺ ـ أَنَّهُ قَالَ " لاَ يَقُومُ أَحَدٌ مِنَ الْمُسْلِمِينَ وَهُوَ حَاقِنٌ حَتَّى يَتَخَفَّفَ " .