I had a fistula; so I asked the prophet ﷺ. He said: offer prayer in standing condition; if you are unable to do so, then in sitting condition: if you are then at your side(i.e, in lying condition).
كَانَ بِيَ النَّاصُورُ فَسَأَلْتُ النَّبِيَّ ﷺ فَقَالَ صَلِّ قَائِمًا فَإِنْ لَمْ تَسْتَطِعْ فَقَاعِدًا فَإِنْ لَمْ تَسْتَطِعْ فَعَلَى جَنْبٍ