(20) باب الصَّبْرِ عَنْ مَحَارِمِ اللَّهِ
Narrated Al-Mughira bin Shu`ba:
The Prophet (ﷺ) 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)?"
Reference: Sahih al-Bukhari 6471
In-book reference: Book 81, Hadith 60
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 8, Book 76, Hadith 478