The Messenger of Allah ﷺ used to pray until his feet became swollen. It was said to him, "Allah has already forgiven your past and future sins, why do you exert yourself so?"He replied, "Should I not be a grateful servant?"
حدثنا أبو هشام الرفاعي محمد بن يزيد حدثنا يحيى بن يمان حدثنا الأعمش عن أبي صالح
كان رسول الله ﷺ يصلي حتى تورمت قدماه فقيل له إن الله قد غفر لك ما تقدم من ذنبك وما تأخر قال أفلا أكون عبدا شكورا
[Sahih] Busiri deemed it strong, but the chain contains a defect. However, it has many corroborating narrations, including what Ibn Khuzayma reported in his Sahih, no. 1184, from the hadith of Muhammad bin Amr, from Abu Salama, from Abu Hurairah, with the same wording, and its chain is hasan. See also the previous hadith.