On the day of Khaybar, a group of the Prophet's ﷺ companions came forward and began saying, "So-and-so is a martyr, so-and-so is a martyr," until they passed by a certain man and said, "So-and-so is a martyr."The Messenger of Allah ﷺ said, "Not at all. I have seen him in the Fire because of a cloak he stole," or "a garment."Then the Messenger of Allah ﷺ said, "Son of Khattab, go and announce to the people that none shall enter Paradise except the believers."Umar said, "So I went out and called, 'Truly, none shall enter Paradise except the believers.'"
حدثنا هاشم بن القاسم حدثنا عكرمة يعني ابن عمار حدثني سماك الحنفي أبو زميل قال حدثني عبد الله بن عباس حدثني
لما كان يوم خيبر أقبل نفر من أصحاب النبي ﷺ فقالوا فلان شهيد فلان شهيد حتى مروا على رجل فقالوا فلان شهيد فقال رسول الله ﷺ كلا إني رأيته في النار في بردة غلها أو عباءة ثم قال رسول الله ﷺ يا ابن الخطاب اذهب فناد في الناس أنه لا يدخل الجنة إلا المؤمنون قال فخرجت فناديت ألا إنه لا يدخل الجنة إلا المؤمنون
Its isnad is sahih. Ikrima bin Ammar Ajli is trustworthy. Ibn Hazm deviated by declaring him extremely daif, indeed nearly accusing him of fabrication, in al-Ihkam 6/24, and I refuted him there. Simak bin Walid Hanafi, Abu Zumayl, with the zay pronounced with a "u" sound, is trustworthy.