Musnad Abu Ya'la al-Mawsili 4:27

Abu Khaythama narrated to us, Mu‘alla ibn Mansur narrated to us, Abu Zubayd ‘Abthar ibn al-Qasim narrated to us, [who] narrated from Mutarrif, from ‘Amir, from Yahya ibn Talha, who said: ‘Umar saw Talha ibn ‘Ubayd Allah [looking] sad. He said: "What is the matter with you?" He said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'I surely know words that no servant says at the time of death except that it relieves him, his color brightens, and he sees what pleases him. Nothing prevented me from asking him about them except the ability to do so.'" ‘Umar said: "I surely know what they are." Talha said: "What are they?" He said: "Do you know a word that is better than the word he invited his uncle to at the time of death?" Talha said: "It is, by Allah, it is." ‘Umar said: "La ilaha illa Allah (There is no god but Allah)."