What is the ruling on the funeral prayer if the Imam makes the Taslim after forgetting the fourth Takbir, and what is the ruling on the prayer of those praying behind him?

The funeral prayer requires four takbīrāt (pronouncements of "Allahu Akbar"). Deliberately omitting any of them invalidates the prayer. If one forgets a takbīrah and remembers it before burial, they should complete it. If a long time has passed, they should restart the prayer. If they remember it after burial and no other prayer was offered for the deceased, they should pray over the grave. There is no prescribed prostration of forgetfulness (sujūd as-sahw) for this. The ruling for the congregants (ma'mūmīn) in this regard is the same as for the Imam.