It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that he said: "We used to say about the killer of a believer, when he died (without repenting), that he is in Hell; and about a person who committed a major sin and died in that state, we also used to say that he is in Hell; until Allah Almighty revealed this verse: 'Indeed, Allah does not forgive that partners be associated with Him, but He forgives what is less than that (of sins) for whom He wills.'"
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated it from Bakr al-Muzani (may Allah have mercy on him) except Ghalib al-Qattan (may Allah have mercy on him), and no one narrated it from Ghalib (may Allah have mercy on him) except Umar bin al-Mughirah (may Allah have mercy on him)."
Hadith Referenceالمعجم الأوسط / باب الألف / 3021
Hadith Gradingمحدثین:إسناده ضعيف لضعف غالب
Hadith Takhrij«قال ابن عدي: غالب في حديثه بعض النكرة و الضعف على أحاديثه بين «الكامل في الضعفاء، ج 7، ص 112»» «أخرجه أبو يعلى فى «مسنده» برقم: 5813، والبزار فى «مسنده» برقم: 5840، والطحاوي فى «شرح مشكل الآثار» برقم: 2137، والطبراني فى «الكبير» برقم: 13332، 13364، 13848، 14028، والطبراني فى «الأوسط» برقم: 5942»