Hadith 932
'Aishah (May Allah be pleased with her) reported:
عن عائشة رضي الله عنها، قالت: قال رسول الله صلى الله عليه وسلم: “ما من ميت يصلي عليه أمة من المسلمين يبلغون مائة كلهم يشفعون له إلا شفعوا فيه“ ((رواه مسلم).
The Messenger of Allah (ﷺ) said, "If a group of Muslims numbering a hundred perform funeral prayer over a dead person, and all of them ask Allah's forgiveness for him, their prayer for him will be accepted." [Muslim].
In plain words
If a hundred Muslims pray over someone who has died and all sincerely ask Allah to forgive them, the Prophet says their prayer will be accepted.
Reference : Riyad as-Salihin 932 In-book reference : Book 6, Hadith 39