كتاب صفة القيامة والجنة والنار
52
Characteristics of the Day of Judgment, Paradise, and Hell
(18)
Chapter: Doing A Lot Of Good Deeds And Striving Hard In Worship
(18)
باب إِكْثَارِ الأَعْمَالِ وَالاِجْتِهَادِ فِي الْعِبَادَةِ ‏‏
Sahih Muslim 2820

A'isha reported that when Allah's Messenger (ﷺ) occupied himself in prayer, he observed such a (long) qiyam (posture of standing in prayer) that his feet were swollen. A'isha said:

Allah's Messenger you do this (in spite of the fact) that your earlier and later sins have been pardoned for you? Thereupon, he said. A'isha should I not prove myself to be a thanksgiving servant (of Allah)?
حَدَّثَنَا هَارُونُ بْنُ مَعْرُوفٍ، وَهَارُونُ بْنُ سَعِيدٍ الأَيْلِيُّ، قَالاَ حَدَّثَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي أَبُو صَخْرٍ، عَنِ ابْنِ قُسَيْطٍ، عَنْ عُرْوَةَ بْنِ الزُّبَيْرِ، عَنْ عَائِشَةَ، قَالَتْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا صَلَّى قَامَ حَتَّى تَفَطَّرَ رِجْلاَهُ قَالَتْ عَائِشَةُ يَا رَسُولَ اللَّهِ أَتَصْنَعُ هَذَا وَقَدْ غُفِرَ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ فَقَالَ ‏ "‏ يَا عَائِشَةُ أَفَلاَ أَكُونُ عَبْدًا شَكُورًا ‏"‏ ‏.‏
Reference : Sahih Muslim 2820
In-book reference : Book 52, Hadith 79
USC-MSA web (English) reference : Book 39, Hadith 6774
  (deprecated numbering scheme)