Musnad Abu Ya'la al-Mawsili 115:59

Abdullah ibn Awn al-Khazzaz narrated to us, Muhammad ibn Bishr narrated to us, from Mis'ar ibn Kidam, from Qatadah, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) stood until his feet or his shins swelled. It was said to him, "Has Allah not forgiven you your past sins and your future ones?" He said, "Shall I not be a grateful servant?"