Sahih al-Bukhari 1130
Narrated Al-Mughira:
The Prophet 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) and he said, "should I not be a thankful slave."
حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا مِسْعَرٌ، عَنْ زِيَادٍ، قَالَ سَمِعْتُ الْمُغِيرَةَ ـ رضى الله عنه ـ يَقُولُ إِنْ كَانَ النَّبِيُّ ﷺ لَيَقُومُ لِيُصَلِّيَ حَتَّى تَرِمُ قَدَمَاهُ أَوْ سَاقَاهُ، فَيُقَالُ لَهُ فَيَقُولُ
" أَفَلاَ أَكُونُ عَبْدًا شَكُورًا ".
Classification
Sahih (Authentic)
References
Sahih al-Bukhari 1130
Sahih al-Bukhari Vol. 2, Book of Night Prayer (Tahajjud), Hadith 230