Musnad Ahmad 1156:27

Abu Mu'awiyah narrated to us, he said: Al-A'mash narrated to us, from Shaqiq, from Umm Salamah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When you are present with a dying person, or a sick person, then say good, for the angels say 'Amin' to what you say." She said: When Abu Salamah died, I came to the Prophet (peace and blessings of Allah be upon him) and said: "O Messenger of Allah, Abu Salamah has died." He said: "Say: O Allah, forgive me and him, and grant me a good successor from him." She said: So I said it, and Allah (the Mighty and Majestic) granted me a successor who was better for me than him: Muhammad (peace and blessings of Allah be upon him).