Musnad Ahmad 2:106

'Abdullah ibn Numayr narrated to us, from Mujalid, from 'Amir, from Jabir ibn 'Abdullah, who said: I heard 'Umar ibn al-Khattab say to Talhah ibn 'Ubaydullah: "What is the matter with me that I see you disheveled and dusty since the Messenger of Allah, peace and blessings of Allah be upon him, passed away? Perhaps the leadership of your cousin has distressed you, O Talhah?" He said: "I seek refuge in Allah. I am more worthy than any of you not to do that. I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'I surely know a word that no man says at the time of death except that his soul finds comfort in it when it departs from his body, and it will be a light for him on the Day of Resurrection.' I did not ask the Messenger of Allah, peace and blessings of Allah be upon him, about it, and he did not inform me of it. That is what has entered upon me [i.e., what is troubling me]." 'Umar said: "I know it." He said: "Praise be to Allah. What is it?" He said: "It is the word he said to his uncle: 'There is no god but Allah' (La ilaha illa Allah)." Talhah said: "You have spoken the truth."