Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said: On the day of Hunayn some Companions were killed, and the people said: So-and-so is a martyr, so-and-so is a martyr, until they passed by a man and said: This one is a martyr. The Messenger of Allah (peace and blessings be upon him) said: "Not at all! Rather, I have seen him in Hell because of a cloak or a sheet he took dishonestly (from the spoils)." Then the Messenger of Allah (peace and blessings be upon him) said: "O Ibn al-Khattab! Go and announce among the people that only the believers will enter Paradise." Sayyiduna Umar (may Allah be pleased with him) said: So I announced among the people that only the believers will enter Paradise.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18204