Musnad Ahmad #1312

It was narrated from Yahya bin Talhah bin `Ubaidullah, from his father, that ‘Umar (رضي الله عنه) saw him looking sad and said: “What is the matter with you, O Abu Muhammad? Perhaps you are upset about your cousin being appointed as caliph?” a word which no one says when he is dying but Allah will relieve him of distress and his colour will brighten.” Nothing prevented me from asking him about it except the fear of not being able to comply with it and I did not ask him about it until he died.” ‘Umar said to him: “I know what it is.” Talhah said to him: “What is it?` ‘Umar 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.”