Ash-Shama'il Al-Muhammadiyah 40:1

Mughirah bin Shu'bah Radiyallahu 'Anhu reports that Rasuluilah Sallallahu 'Alayhi Wasallam performed such lengthy nafl prayers, that his mubaarak legs became swollen. The Sahaabah said :

"You undergo such great difficulties, where Allah had forgiven your past and the future sins. "Rasulullah Sallallahu 'Alayhi Wasallam said: "(When Allah Ta'aala has blessed me so much) should I not be a grateful servant?"