Saadi Murriyah reported,

Umar passed by Talha after the death of the Messenger of Allah ﷺ and said, "Why do I see you so downcast? Has your cousin's rule troubled you?"Talha replied, "No, but I once heard the Messenger of Allah ﷺ say, 'I know a word which, if anyone says it at the moment of his death, will be a light for his record, and his body and soul will find comfort through it at death.' Yet I did not ask him about it before he passed away."Umar said, "I know it. It is the very word he wanted his uncle to say. Had he known of anything more saving for him than it, he would have commanded him to say it."

Ibn Majah 3795

Sahih

حدثنا هارون بن إسحق الهمداني حدثنا محمد بن عبد الوهاب عن مسعر عن إسمعيل بن أبي خالد عن الشعبي عن يحيى بن طلحة

عن أمه سعدى المرية قالت

مر عمر بطلحة بعد وفاة رسول الله ﷺ فقال ما لك كئيبا أساءتك إمرة ابن عمك قال لا ولكن سمعت رسول الله ﷺ يقول إني لأعلم كلمة لا يقولها أحد عند موته إلا كانت نورا لصحيفته وإن جسده وروحه ليجدان لها روحا عند الموت فلم أسأله حتى توفي قال أنا أعلمها هي التي أراد عمه عليها ولو علم أن شيئا أنجى له منها لأمره

ابن ماجه 3795صحيح
Contents
Reference
Commentary
Ayat
Collection
Sunan Ibn Majah
Book
Manners
Chapter
Virtue of "there is no god but Allah"
Numbering
Darussalam 3795
Ibn Majah 3795