Musnad Ahmad 1384
It was narrated from Yahya bin Talhah that his father said:
`Umar(رضي الله عنه) saw Talhah bin `Ubaidullah 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: `I 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.` Umar (رضي الله عنه) said: “I know what it is.” Talhah said: “What is it?” ’Umar(رضي الله عنه) 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.”
حَدَّثَنَا أَسْبَاطٌ، حَدَّثَنَا مُطَرِّفٌ، عَنْ عَامِرٍ، عَنْ يَحْيَى بْنِ طَلْحَةَ، عَنْ أَبِيهِ، قَالَ رَأَى عُمَرُ طَلْحَةَ بْنَ عُبَيْدِ اللَّهِ ثَقِيلًا فَقَالَ مَا لَكَ يَا أَبَا فُلَانٍ لَعَلَّكَ سَاءَتْكَ إِمْرَةُ ابْنِ عَمِّكَ يَا أَبَا فُلَانٍ قَالَ لَا إِلَّا أَنِّي سَمِعْتُ مِنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ حَدِيثًا مَا مَنَعَنِي أَنْ أَسْأَلَهُ عَنْهُ إِلَّا الْقُدْرَةُ عَلَيْهِ حَتَّى مَاتَ سَمِعْتُهُ يَقُولُ إِنِّي لَأَعْلَمُ كَلِمَةً لَا يَقُولُهَا عَبْدٌ عِنْدَ مَوْتِهِ إِلَّا أَشْرَقَ لَهَا لَوْنُهُ وَنَفَّسَ اللَّهُ عَنْهُ كُرْبَتَهُ قَالَ فَقَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ إِنِّي لَأَعْلَمُ مَا هِيَ قَالَ وَمَا هِيَ قَالَ تَعْلَمُ كَلِمَةً أَعْظَمَ مِنْ كَلِمَةٍ أَمَرَ بِهَا عَمَّهُ عِنْدَ الْمَوْتِ لَا إِلَهَ إِلَّا اللَّهُ قَالَ طَلْحَةُ صَدَقْتَ هِيَ وَاللَّهِ هِيَ‏.‏