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  

ʿUmarؓ saw Talhah bin ʿUbaidullah looking upset and said: “What is the matter with you, O Father of so and so? Perhaps your cousin being appointed as caliph has upset you, O Father of so and so?” He said: “No, but I heard a Hadeeth from the Messenger of Allah ﷺ and nothing prevented me from asking him about it except the fear of not being able to comply with it sand I did not ask him about it until he died. I heard him say: ʿI know a word which no one says at the time of death but his colour will brighten and Allah will relieve him of his distress.ʿ Umar ؓ said: “I know what it is.” Talhah said: “What is it?” ’Umarؓ said: “Do you know any word that is greater than the word he enjoined his uncle to say when he was dying, La ilaha illallah?” Talhah said: “You are right. By Allah, that is what it is.” (Using translation from Aḥmad 1384)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ إِنِّي لَأَعْلَمُ كَلِمَةً لَا يَقُولُهَا عَبْدٌ عِنْدَ مَوْتِهِ إِلَّا نَفَّسَ اللهُ عَنْهُ كَرْبَهُ فَمَا مَنَعَنِي أَنْ أَسْأَلَهُ عَنْهَا إِلَّا الْقُدْرَةُ عَلَيْهَا حَتَّى مَاتَ قَالَ إِنِّي لَأَعْلَمُهَا هَلْ تَعْلَمُ مِنْ كَلِمَةٍ هِيَ أَعْظَمُ مِنْ كَلِمَةٍ أَمَرَ بِهَا عَمَّهُ «لَا إِلَهَ إِلَّا اللهُ» قَالَ هِيَ وَاللهِ هِيَ  

"عَنْ حُمْرَانَ أَنَّ عُثْمَانَ قَالَ: سَمِعْتُ رَسُولَ الله ﷺ يقولُ: إِنِّى لأَعْلَمُ كَلِمَةً لَا يَقُولُهَا عَبْدٌ حَقًا مِنْ قَلْبِهِ يَمُوتُ عَلَى ذَلِكَ إِلَّا حَرَّمَهُ الله عَلَى النَّارِ، فَقَالَ عُمَرُ بْنُ الخَطَّابِ: أَنّا أُحَدِّثُكُمْ مَا هِىَ: هِىَ كَلِمَةُ الإِخْلَاصِ الَّتِى أَلْزَمَهَا الله مُحَمّدًا وَأَصْحَابَهُ، وَهِىَ كَلِمَةُ التَّقْوَى الَّتى أَلَاصَ عَلَيْها نَبِىُّ الله عمَّه أَبا طَالِبٍ عِنْدَ الْمَوْتِ: شَهادةُ أَنْ لَا إِلَهَ إِلَّا الله".