Shama'il Muhammadiyah #252

Al-Mughira ibn Shu'ba said (may Allah be well pleased with him): "Allah’s Messenger (Allah bless him and give him peace) 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?'”