Uthman bin Affan reported,
I heard the Messenger of Allah ﷺ say, "I know of a word that no servant utters truly from his heart except that he is made forbidden to the Fire."Umar bin Khattab said to him, "Let me tell you what it is. It is the word of sincerity which Allah 
bound upon Muhammad and his Companions. It is the word of piety which the Prophet of Allah ﷺ urged upon his uncle Abu Talib at the moment of death, the testimony that there is no god but Allah."
Azami 88
Hasanعن عثمان بن عفان قال
سمعت رسول الله ﷺ يقول: إني لأعلم كلمة لا يقولها عبد حقا من قلبه إلا حرم على النار. فقال له عمر بن الخطاب: أنا أحدثك ما هي، هي كلمة الإخلاص التي ألزمها الله تبارك وتعالى محمدا وأصحابه، وهي كلمة التقوى التي ألاص عليها نبي الله ﷺ عمه أبا طالب عند الموت: شهادة أن لا إله إلا الله.
Ahmad narrated it (447), and Ibn Hibban graded it sahih (204), as did Hakim (1/351), all of them through the route of Abdul-Wahhab bin Ata Khafaf, who said, Saeed narrated to us, from Qatada, from Muslim bin Yasar, from Humran bin Aban, that Uthman bin Affan said (then he mentioned the hadith), and the wording is Ahmad's.Hakim said, "Sahih according to the standard of the two Shaykhs."I say, its chain is hasan because of Abdul-Wahhab bin Ata Khafaf, for there is disagreement about him, though he is hasan al-hadith. Saeed here is Ibn Abu Aruba, who became confused in his later years, but Abdul-Wahhab bin Ata heard from him before the confusion set in, and Saeed bin Abu Aruba is considered among the most reliable transmitters when it comes to Qatada.