What is the ruling regarding a man who died and left instructions to be buried in a coffin?

Most scholars dislike burying the deceased in a coffin because it is an innovation (bid'ah) unknown during the time of the Prophet (peace be upon him) and his Companions. It goes against their guidance and resembles the practices of worldly people. Furthermore, the earth is more absorbent of the deceased's bodily fluids. However, if there is a necessity, such as wet or soft ground, fear of wild animals digging up the grave, or the deceased's body being so decomposed that only a coffin can hold it together, then it is not disliked.

The deceased's will to be buried in a coffin is not to be carried out except in these specific cases.