Can the funeral prayer be performed inside a mosque?

The funeral prayer is generally performed outside the mosque unless there is a valid excuse. However, if there is a reason such as rain, mud, or cold, there is no objection to performing it inside the mosque (el-Fetâva’l-Hindiyye, 1/165). According to the Shafi'i school, if there is no concern about the mosque being soiled, it is recommended (mustahabb) to perform this prayer in the mosque (Nevevî, el-Mecmû’, 5/213). When Sa’d b. Abî Waqqâs passed away, Aisha (ra) requested that the funeral be brought to the mosque so she could join the prayer, but the companions did not approve of her request. Upon this, Aisha said, “How quickly people forget! The Messenger of Allah (pbuh) performed the funeral prayer of Suhayl b. Bayda in the mosque.” (Muslim, Janâ’iz, 99 [973])

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu