كان النبي صلى الله عليه واله وسلم
يصلي حتى ترم ـ أو تنتفخ ـ قدماه فيقال له، فيقول:
‏"‏ أفلا أكون عبدا شكورا ‏"‏‏

البخاري
الرقاق 6549


Narrated Al-Mughira bin Shu'ba (may Allah be pleased with him):
The Prophet (peace be upon him) used to pray so much that his feet used to become edematous or swollen, and when he was asked as to why he prays so much, he would say,

"Shall I not be a thankful slave (to Allah
)?"

Bukhari Volume 8, Book 76, Number 478