ENOfficial
‘Imran b. Husain reported God’s Messenger as saying, “Pray standing, but if you are unable, do it sitting; and if you are unable to do that, do it lying on your side.” Bukhari transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ عِمْرَانَ بْنِ حُصَيْنٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «صَلَّى اللَّهُ عَلَيْهِ وَسلم قَائِمًا فَإِنْ لَمْ تَسْتَطِعْ فَقَاعِدًا فَإِنْ لَمْ تستطع فعلى جنب» . رَوَاهُ البُخَارِيّ
sunnah.com