The Quran Verse
Surah 14:27:
Allah keeps firm those who believe, with the firm word, in worldly life and in the Hereafter...
While the verse itself is vague, the Hadith (Sahih Bukhari 4699) explicitly interprets this "firm word" as the testimony a person gives in the grave when questioned by the angels Munkar and Nakir.
This is an example of the "Islamization" of the afterlife. The concept of the "Punishment of the Grave" and the interrogation by angels is absent from the Torah and the New Testament.
Critics argue this reflects the influence of Zoroastrian and later Jewish folk beliefs about the soul's journey after death that were circulating in the Near East during the 7th century.