His friend became an atheist then he died. Can he offer the funeral prayer for him and say du’aa’ for him?

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Check below answers in case you are looking for other related questions:
Following the funeral processions of those who worshipped graves
Following the funeral procession of a kaafir

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Related Answers:
Whoever washes the dead let him do ghusl
Ruling on giving clothing or money to the family of the deceased instead of giving them food
Raising the voice during a funeral
Following the funeral processions of those who worshipped graves
Following the funeral procession of a kaafir

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