How the Holy Prophet s.a. used to offer Salat

اَلْمُغِيْرَةُ رَضِىَ اللهُ عَنْهُ يَقُوْلُ إِنْ كَانَ النَّبِيُّ صَلًّى اللهُ عَلَيْهِ وَسَلَّمَ لَيَقُومُ لِيُصَلِّيَ حَتَّى تَرِمُ قَدَمَاهُ أَوْ سَاقَاهُ، فَيُقَالُ لَهُ فَيَقُولُ ‏أَفَلاَ أَكُوْنُ عَبْدًا شَكُوْرًا ‏

Hazrat Al-Mughira^ra narrates, “The Holy Prophet^sa used to stand in the prayer or pray till both his feet or legs swelled. He was asked why he offered such an unbearable prayer, to which he replied, ‘Should I not be a thankful servant?’”

(Sahih al-Bukhari, Kitab al-Tahajud, Hadith 1130)