It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "When you are present with a dying or deceased person, say what is good, for the angels say Amin to what you say."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20026