«إذا أقعد المؤمن في قبره أتي ثم شهد أن لا إله إلا الله وأن محمد رسول الله فذلك قوله: {يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ} »
The Prophet (peace and blessings be upon him) said:
"When the believer is made to sit up in his grave and (the angels) come to him, he bears witness that there is no true god except Allah and that Muhammad (peace and blessings be upon him) is the Messenger of Allah. That is the meaning of the saying of Allah Almighty: 'Allah keeps firm those who believe with the firm word.' [Surah Ibrahim: 27]"
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 366