“The prophet
kept standing (in prayer) so long that the skin of his feet would crack. I asked him: ‘Why do you do this, while you have been forgiven of your former and latter sins?’ He said, ‘Should I not be a grateful slave of Allah?’” (Al Bukhari and Muslim)



visited me and Fatimah رضي الله عنه one night and said, ‘Do you not observe prayer (at night)?’”