The Messenger of Allah ﷺ prayed until his feet became swollen. It was said to him, "Do you burden yourself with this when Allah has already forgiven your past and future sins?"He replied, "Should I not be a grateful servant?"
حدثنا قتيبة وبشر بن معاذ العقدي قالا حدثنا أبو عوانة عن زياد بن علاقة
صلى رسول الله ﷺ حتى انتفخت قدماه فقيل له أتتكلف هذا وقد غفر لك ما تقدم من ذنبك وما تأخر قال أفلا أكون عبدا شكورا
Agreed upon [by Bukhari and Muslim]. Muslim narrated it in "The Traits of the Hypocrites," chapter "Doing Many Deeds and Striving Hard in Worship," no. 819, from Qutayba, and Bukhari, no. 1130, both through the hadith of Ziyad bin Alaqa.There are also narrations on this subject from Hurairah [Nasai, no. 1646] and Ayesha [Bukhari, no. 4837, and Muslim, no. 2820].