Musnad Abi Ya'la 642 — from his mother, Sayyidah Su'da al-Murriyyah

Yahya bin Talhah (may Allah have mercy on him) narrates from his mother, Sayyidah Su'da al-Murriyyah (may Allah be pleased with her), that she said: After the sorrowful passing of the Messenger of Allah (peace and blessings be upon him), Sayyiduna Umar (may Allah be pleased with him) passed by Sayyiduna Talhah (may Allah be pleased with him) and asked: "What is the reason that I see you so grief-stricken? Has the leadership of your cousin displeased you?" He replied: "No, (it is not that,) rather I heard the Messenger of Allah (peace and blessings be upon him) saying: 'Indeed, I know a word that whoever utters it at the time of his death, it will be a light for his record of deeds, and his body and his soul will find comfort and relief through it at the hardship of death.' (Alas, I was not able to ask about that word.)" Sayyiduna Umar (may Allah be pleased with him) said: "I know that word. It is the very word which he (peace and blessings be upon him) asked his uncle to accept (at the time of his death); and if he (peace and blessings be upon him) had known of anything more saving for him than this word, he (peace and blessings be upon him) would certainly have commanded him with it."