Regarding "Allah keeps firm those who believe with the firm word in the worldly life and in the Hereafter" [Ibrahim 14:27], he said, "It was revealed concerning the punishment of the grave."
أخبرنا إسحق بن منصور قال حدثنا عبد الرحمن عن سفيان عن أبيه عن خيثمة
{يثبت الله الذين آمنوا بالقول الثابت في الحياة الدنيا وفي الآخرة} قال نزلت في عذاب القبر
Muslim narrated it in "Paradise and Its Delights," in the chapter on the presentation of the deceased's abode in Paradise or Hell before him, etc., hadith no. 74/2871, from the hadith of Abdul-Rahman bin Mahdi, with this wording. It is also found in Kubra, hadith no. 2183.