Ash-Shama'il Al-Muhammadiyah 262
It is also reported from Abu Huraira, may Allah be well pleased with him that:
Allah’s Messenger (Allah bless him and give him peace) used to stand performing the ritual prayer until his feet had begun to swell, so he would be asked: “O Messenger of Allah, must you do this, when Allah has already forgiven you your former and your latter sins?” He replied: “Shall I not be a thankful servant?”
حَدَّثَنَا عِيسَى بْنُ عُثْمَانَ بْنِ عِيسَى بْنِ عَبْدِ الرَّحْمَنِ الرَّمْلِيُّ، قَالَ‏:‏ حَدَّثَنَا عَمِّي يَحْيَى بْنُ عِيسَى الرَّمْلِيُّ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ‏:‏ كَانَ رَسُولُ اللهِ صلى الله عليه وسلم يَقُومُ يُصَلِّي حَتَّى تَنْتَفِخَ قَدَمَاهُ فَيُقَالُ لَهُ‏:‏ يَا رَسُولَ اللهِ، تَفْعَلُ هَذَا وَقَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ‏؟‏، قَالَ‏:‏ أَفَلا أَكُونُ عَبْدًا شَكُورًا‏.‏