This verse: "Allah grants steadfastness to those who believe with firm word," was revealed in connection with the torment of the grave. It would be said to him: Who is your Lord? And he would say: Allah is my Lord and Muhammad is my Apostle ﷺ, and that is (what is implied) by the words of Allah, the Exalted: "Allah keeps steadfast those who believe with firm word in this world and in the Hereafter."  

عَنِ النَّبِيِّ ﷺ قَالَ { يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ} قَالَ نَزَلَتْ فِي عَذَابِ الْقَبْرِ فَيُقَالُ لَهُ مَنْ رَبُّكَ فَيَقُولُ رَبِّيَ اللَّهُ وَنَبِيِّيَ مُحَمَّدٌ ﷺ فَذَلِكَ قَوْلُهُ ﷻ { يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الآخِرَةِ}  

"Allah will keep firm those who believe, with the world that stands firm in this world, and in the Hereafter. This was revelated concerning the torment in the grave. It will be said to him (the deceased: 'Who is your Lord?' and he will say: 'My Lord is Allah and my Prophet is Muhammad. That is what is (the meaning of) His saying: Allah will keep firm those who believe, with the word that stands firm in this world, and in the Hereafter".  

عَنِ النَّبِيِّ ﷺ قَالَ { يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الآخِرَةِ } قَالَ نَزَلَتْ فِي عَذَابِ الْقَبْرِ يُقَالُ لَهُ مَنْ رَبُّكَ فَيَقُولُ رَبِّيَ اللَّهُ وَدِينِي دِينُ مُحَمَّدٍ ﷺ فَذَلِكَ قَوْلُهُ { يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الآخِرَةِ }  

“Allah will keep firm those who believe, with the word that stands firm.” [14:27] This has been revealed concerning the torment of the grave. It will be said to him: ‘Who is your Lord?’ He will say: ‘My Lord is Allah, and my Prophet is Muhammad.’ This is what Allah says: Allah will keep firm those who believe, with the word that stands firm in this world (i.e. they will keep on worshipping Allah Alone and none else), and in the Hereafter (i.e., at the time of questioning in the grave).’” [14:27]  

عَنِ النَّبِيِّ ﷺ قَالَ {يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ } قَالَ نَزَلَتْ فِي عَذَابِ الْقَبْرِ يُقَالُ لَهُ مَنْ رَبُّكَ فَيَقُولُ رَبِّيَ اللَّهُ وَنَبِيِّي مُحَمَّدٌ فَذَلِكَ قَوْلُهُ {يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الآخِرَةِ}  

[Machine] Narrated by the Prophet ﷺ , he said: "The punishment of the grave is mentioned, and it is said to him, 'Who is your Lord?' He replies, 'Allah is my Lord, and Muhammad is my Prophet.' This is in accordance with Allah's saying, 'Allah will establish in steadfastness those who have believed with the firm word in worldly life.' (Surah Ibrahim, 27). This means the Muslim."  

عَنِ النَّبِيِّ ﷺ قَالَ ذَكَرَ عَذَابَ الْقَبْرِ قَالَ يُقَالُ لَهُ مَنْ رَبُّكَ؟ فَيَقُولُ اللهُ رَبِّي وَنَبِيِّي مُحَمَّدٌ فَذَلِكَ قَوْلُهُ {يُثَبِّتُ اللهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا} [إبراهيم 27] يَعْنِي بِذَلِكَ الْمُسْلِمَ  

“Allah will keep firm those who believe, with the word that stands firm.” [14:27] This has been revealed concerning the torment of the grave. It will be said to him: ‘Who is your Lord?’ He will say: ‘My Lord is Allah, and my Prophet is Muhammad.’ This is what Allah says: Allah will keep firm those who believe, with the word that stands firm in this world (i.e. they will keep on worshipping Allah Alone and none else), and in the Hereafter (i.e., at the time of questioning in the grave).’” [14:27] (Using translation from Ibn Mājah 4269)  

عَنِ النَّبِيِّ ﷺ قَالَ {يُثَبِّتُ اللهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا} [إبراهيم 27] قَالَ نَزَلَتْ فِي عَذَابِ الْقَبْرِ يُقَالُ لَهُ مَنْ رَبُّكَ؟ فَيَقُولُ رَبِّيَ اللهُ وَنَبِيِّي مُحَمَّدٌ فَذَلِكَ قَوْلُهُ {يُثَبِّتُ اللهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الْآخِرَةِ} [إبراهيم 27]