I heard the Messenger of Allah ﷺ say: ʿI know a word which no one says, sincerely from the heart, but he will be forbidden to the Fire.” ʿUmar bin al-Khattab ؓ said to him: I will tell you what it is: it is the word of al-ikhlas by means of which Allah, may He be blessed and exalted, caused Muhammad ﷺ and his companions to prevail and it is the word of taqwa that the Prophet ﷺ of Allah urged his uncle Abu Talib to say when he was dying, the testimony that there is no god but Allah.  

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ إِنِّي لَأَعْلَمُ كَلِمَةً لَا يَقُولُهَا عَبْدٌ حَقًّا مِنْ قَلْبِهِ إِلَّا حُرِّمَ عَلَى النَّارِ فَقَالَ لَهُ عُمَرُ بْنُ الْخَطَّابِ أَنَا أُحَدِّثُكَ مَا هِيَ؟ هِيَ كَلِمَةُ الْإِخْلاصِ الَّتِي أَلْزَمَهَا اللهُ تَبَارَكَ وَتَعَالَى مُحَمَّدًا ﷺ وَأَصْحَابَهُ وَهِيَ كَلِمَةُ التَّقْوَى الَّتِي أَلَاصَ عَلَيْهَا نَبِيُّ اللهِ ﷺ عَمَّهُ أَبَا طَالِبٍ عِنْدَ الْمَوْتِ شَهَادَةُ أَنْ لَا إِلَهَ إِلَّا اللهُ  

I heard the Messenger of Allah ﷺ say: ʿI know a word which no one says, sincerely from the heart, but he will be forbidden to the Fire.” ʿUmar bin al-Khattab ؓ said to him: I will tell you what it is: it is the word of al-ikhlas by means of which Allah, may He be blessed and exalted, caused Muhammad ﷺ and his companions to prevail and it is the word of taqwa that the Prophet ﷺ of Allah urged his uncle Abu Talib to say when he was dying, the testimony that there is no god but Allah. (Using translation from Aḥmad 447)   

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ «إِنِّي لَأَعْلَمُ كَلِمَةً لَا يَقُولُهَا عَبْدٌ حَقًّا مِنْ قَلْبِهِ فَيَمُوتُ إِلَّا حُرِّمَ عَلَى النَّارِ» فَقُبِضَ رَسُولُ اللَّهِ ﷺ وَلَمْ يُخْبِرْنَاهَا فَقَالَ عُمَرُ بْنُ الْخَطَّابِ أَنَا أُخْبِرُكَ بِهَا هِيَ كَلِمَةُ الْإِخْلَاصِ الَّتِي أَمَرَ بِهَا رَسُولُ اللَّهِ ﷺ عَمَّهُ أَبَا طَالِبٍ عِنْدَ الْمَوْتِ شَهَادَةُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَهِيَ الْكَلِمَةُ الَّتِي أَكْرَمَ اللَّهُ بِهَا مُحَمَّدًا وَأَصْحَابَهُ