"Messenger of Allah (S) performed Salat until his feet were swollen, so it was said to him: 'You burden yourself like this, while your past and future sins have been forgiven?' He said: 'Shouldn't I be a grateful worshipper?'"  

صَلَّى رَسُولُ اللَّهِ ﷺ حَتَّى انْتَفَخَتْ قَدَمَاهُ فَقِيلَ لَهُ أَتَتَكَلَّفُ هَذَا وَقَدْ غُفِرَ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ قَالَ أَفَلاَ أَكُونُ عَبْدًا شَكُورًا قَالَ وَفِي الْبَابِ عَنْ أَبِي هُرَيْرَةَ وَعَائِشَةَ