It is narrated on the authority of 'Uthman that the Messenger of Allah (ﷺ) said. He who died knowing (fully well) that there is no god but Allah entered Paradise
Hadith Referenceصحيح مسلم / كتاب الإيمان / 26
Hadith Gradingمحدثین:أحاديث صحيح مسلم كلها صحيحة
Hadith Takhrij«أحاديث صحيح مسلم كلها صحيحة ، انفرد به مسلم - انظر ((تحفة الاشراف)) برقم (9798) »
It is narrated on the authority of Humran that he heard 'Uthman saying this: I heard the Messenger of Allah (ﷺ) uttering these words (as stated above).
Hadith Referenceصحيح مسلم / كتاب الإيمان / 26
Hadith Gradingمحدثین:أحاديث صحيح مسلم كلها صحيحة
Hadith Takhrij«أحاديث صحيح مسلم كلها صحيحة ، انفرد به مسلم - انظر ((التحفة)) برقم (9798) »
Hadith Commentary:Benefits and Issues: The Ahl al-Sunnah and the people of truth are in agreement that whoever dies upon tawhid (the oneness of Allah) is destined for Paradise, provided he has abstained from sins. The correct view is that such a person will enter Paradise directly, but if he committed major sins (kabirah) and was not granted the ability to repent, then it is up to Allah’s will: He may forgive his sins and admit him to Paradise, or He may admit him to Hell in accordance with his sins, purify him from them, and then bring him into Paradise. In any case, with regard to the final outcome, he is destined for Paradise. For the affirmation and testimony of tawhid, it is necessary to have certainty and faith in the Messengership and the Hereafter; these are inseparably linked together.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 136
‘Uthman b. ‘Affan reported God's messenger as saying, “Whoever dies knowing that there is no god but God will enter paradise." Muslim transmitted it.
Hafiz Zubair Ali Zai
Fiqh al-Hadith: ➊ Salvation is dependent solely upon having faith in Allah and His Messenger, and acting upon the Qur’an and Hadith. Without Tawhid (monotheism) and Sunnah, there is nothing but darkness. Only the one who affirms Tawhid will enter Paradise. ➋ Before Tawhid, it is necessary to have knowledge of it, and then to affirm it with the heart, the tongue, and the body—this alone constitutes faith (iman).
Source: Adwa al-Masabih fi Tahqiq Mishkat al-Masabih, Page: 37