I heard the Messenger of Allah (ﷺ) saying: He who dies associating anything with Allah would enter the Fire (of Hell). 'Abdullah b. Mas'ud said: I say that he who died without associating anything with Allah entered Paradise.
The Book of Faith - Sahih Muslim 92
This narration from the Prophet Muhammad (ﷺ) establishes the fundamental Islamic doctrine of Tawhid (Divine Unity). The statement "He who dies associating anything with Allah would enter the Fire" serves as the primary criterion distinguishing believers from disbelievers in the Hereafter.
Scholarly Commentary on the Hadith
The Prophet's declaration establishes that Shirk (associating partners with Allah) nullifies all good deeds and guarantees eternal punishment. This includes both major Shirk (worshipping other deities) and minor Shirk (showing off in worship, excessive oath-taking by other than Allah).
Ibn Mas'ud's complementary statement "he who died without associating anything with Allah entered Paradise" demonstrates the Companions' deep understanding that pure Tawhid is the key to salvation. This doesn't negate the necessity of performing obligatory acts, but emphasizes that Tawhid is the foundation upon which all other acts are accepted.
Legal and Theological Implications
Classical scholars explain that this hadith establishes the absolute invalidity of any deed accompanied by Shirk. The protection of Tawhid requires constant vigilance against subtle forms of polytheism in intention, speech, and action.
The consensus among Ahl al-Sunnah scholars is that whoever dies upon pure Islamic monotheism - even with sins - will ultimately enter Paradise, either directly or after purification, provided they did not die in a state of major Shirk which removes one from the fold of Islam entirely.