Al-Mughirah bin Shu'bah narrated:"Allah's Messenger (S) performed Salat until his feet were swollen, so it was said to him: 'You burden yourself like this, while your past and future sins have been forgiven?' He said: 'Shouldn't I be a grateful worshipper?
Opening the collection...
“Read in the name of your Lord who created.” 96:1
“My Lord, increase me in knowledge.” 20:114
“So remember Me; I will remember you.” 2:152
“Indeed, with hardship comes ease.” 94:6