Al-Mughira ibn Shu'ba said (may Allah be well pleased with him):

"Allah’s Messenger (ﷺ) performed the ritual prayer until his feet became swollen, so he was asked: 'Must you burden yourself with this, when Allah has already forgiven you your former and your latter sins?' He replied: 'Shall I not be a thankful servant?'”

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَبِشْرُ بْنُ مُعَاذٍ، قَالا‏:‏ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ زِيَادِ بْنِ عِلاقَةَ، عَنِ الْمُغِيرَةِ بْنِ شُعْبَةَ، قَالَ‏:‏ صَلَّى رَسُولُ اللهِ صلى الله عليه وسلم، حَتَّى انْتَفَخَتْ قَدَمَاهُ، فَقِيلَ لَهُ‏:‏ أَتَتَكَلَّفُ هَذَا، وَقَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ‏؟‏ قَالَ‏:‏ أَفَلا أَكُونُ عَبْدًا شَكُورًا‏.‏