(Why do you undergo so much hardship despite the fact that) Allah has pardoned for you your earlier and later sins? Thereupon he said: May I not (prove myself) to be a grateful servant (of Allah)?  

أَنَّ النَّبِيَّ ﷺ صَلَّى حَتَّى انْتَفَخَتْ قَدَمَاهُ فَقِيلَ لَهُ أَتَكَلَّفُ هَذَا وَقَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ فَقَالَ أَفَلاَ أَكُونُ عَبْدًا شَكُورًا  

Allah's Apostle ﷺ kept standing in prayer (for such long hours) that his feet were swollen. They (his Companions) said: Verily, Allah has pardoned for thee the earlier and the later of thine sins. Thereupon he said: Should I not prove myself to be a grateful servant (of Allah)?  

سَمِعَ الْمُغِيرَةَ بْنَ شُعْبَةَ يَقُولُ قَامَ النَّبِيُّ ﷺ حَتَّى وَرِمَتْ قَدَمَاهُ قَالُوا قَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ قَالَ أَفَلاَ أَكُونُ عَبْدًا شَكُورًا  

The Messenger of Allah ﷺ used to stand up after performing prayer until his feet were swollen. ʿĀʾishah said, "O Messenger of Allah, do you do this while your past and future sins have been forgiven?" He replied, "O ʿĀʾishah, should I not be a grateful servant?"  

كَانَ رَسُولُ اللَّهِ ﷺ 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؟»