Shama-il Tirmidhi Chapter 39, Hadith Number 2 (249).

Abu Hurayrah Radiyallahu ‘Anhu says: “Rasulullah Sallallhu ‘Alayhi Wasallam performed so many nawaafil prayers that his legs swelled. Someone said to him, you take so many pains, whereas you have been given the good news that your past and present sins have been forgiven? He replied: “Should I not be grateful servant”.

A detailed narration has been narrated from Sayyiditina ‘Aayeshah Radiyallhu ‘Anha regarding this thanks-giving. Sayyidina ‘Ataa Radiyallahu ‘Anhu says: “I once requested ‘Aayeshah to a surprising incident of Rasulullah Sallallhu ‘Alayhi Wasallam?. ‘She replied: ‘Which act of Rassulullah Sallallahu ‘Alayhi Wasallam was such that it was not surprising’. Thereafter she said: ‘One night Rasulullah Sallallhu ‘Alayhi Wasallam returned home to sleep and slept with me in my blanket. After a little while, as he was sleeping he said: ‘Forget it, let me worship my creator’. Saying this he got up, performed wudhu and began to perform salaah. He began weeping till the tears flowed on to his mubaarak chest. He then performed ruku’, and continued crying in this posture. Then performed sajdah and kept on weeping in this posture too. He stood up from the sajdah and remained crying. He remained in this state till the morning when Bilaal came to call out the adhaan. I said: O Messenger of Allah, why did you cry so much? Allah Ta’aala has forgiven all your past and future sins’. Sayyidina Rasulullah Sallallhu ‘Alayhi Wasallam replied: ‘Should I not be a thankful servant of Allah? Then said: ‘Why should I not do so, when these aayaat were revealed to me today, and recite the aayaat of the last ruku’ of Sura Aali ‘Imran'”.