Sayyiduna al-Nawwas bin Sam'an (may Allah be pleased with him) narrated that he heard the Prophet (peace and blessings be upon him) say: "Whoever dies in a state in which he associates nothing with Allah Almighty as a partner, forgiveness becomes his due."
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir, and there is no harm in its chain.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الإيمان / 26