الْمُغِیرَۃَ رَضِیَ اللہُ عَنْہُ یَقُولُ اِنْ کَانَ النَّبِیُّ صَلَّی اللہُ عَلَیْہِ وَسَلَّمَ لَیَقُوْمُ لِیُصَلِّیَ حَتَّی تَرِمُ قَدَمَاہُ أَوْسَاقَاہُ، فَیُقَالُ لَہُ فَیَقُوْلُ أَفَلَا أَکُونُ عَبْدًا شَکُورًا
Hazrat Al-Mughirara narrated that the Prophet, peace and blessings of Allah be upon him, 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 said, “Should I not be a thankful servant [to Allah]?”
(Sahih al-Bukhari, Kitab al-Tahajud, Hadith 1130)