Mishkat al-Masabih #121

‘A’isha told of a Jewess who visited her and mentioned the punishment in the grave adding, “May God preserve you from the punishment of the grave!” ‘A’isha asked God’s messenger about the subject and he said, “Yes, the punishment in the grave is real.” ‘A’isha said, “After that I never saw God’s messenger observing a prayer without seeking God’s protection from the punishment in the grave.” (Bukhari and Muslim.)