Funeral Salat, is a duty for the Muslims. The rules for this Salat are as follows:
The dead person must be a Muslim. No Funeral Salat is performed for the dead person that is not publicly known as Muslim. There must be sufficient proof or witness about the religion of the dead person.
The dead person is washed and shrouded in a clean shroud.
The dead person must be in front of the imam and the crowd.
The whole part of the corpse of the dead person, or most of the corpse must be present. If most of the corpse or the head is not present, the corpse is not washed and the funeral Salat is not performed. Such a corpse is shrouded and buried without a funeral Salat.
Performing The Funeral Salat:
The funeral Salat is performed standing on the foot with 4 tekbirs. There are no bows or prostrations.
The imam (prayer leader) stands next to the dead persons chest level. The crowd stands behind him. The imam tells the crowd whether the dead person is a man or a woman, the intend is done according to this. That is, the intend is done as; “For Salat to Allah, for pray to the dead, I go along with the imam” and tekbir is brought. In the first tekbir, the hands are rose to the level of the ears, and then the hands are wrapped under the hub. Subhanaka is read with the words “ve celle senauke”.
After that, a second tekbir is brought without rising the hands. These tekbirs are brought by the imam openly, by the crowd secretly. ” Allahumma salli and Allahumma barik prays” are read. Then, the third tekbir is brought and funeral pray is read.
The ones that do not know funeral pray, may read at this part “Allahumma inni nestaiynuke”; that is Kunut Prays, or Fatiha for intenton of a pray to the dead. Then, the fourth tekbir is brought and the hands are freed and selam is given.
Most people, in the fourth tekbir of Funeral Salat, either do not free their hands or free their right hands at giving selam to the right side, freeing left hand at giving selam to the left side.
Both of these, are wrong. After bringing the fourth tekbir freeing the hands and then giving selam to the both sides is true. Because, the hands are wrapped at the standings in which there is a sunnah. On the standings where there is no sunna, the hands are left free. (D, 1/53)
During the Funeral Salat, some people rise their heads when the imam brings tekbir. This is too, a wrong behaviour. The head, or another part of the body must not be moved during the pray.
Source: Muhtasar Ilmihal (Resimli Namaz Hocasi) 67. Baski, Hasan Arikan, https://islamqa.info