Muslims believe that the present life is a trial in preparation for the next realm of existence. When a Muslim dies, he or she is washed and wrapped in a clean, white cloth (usually by a family member) and buried after a special prayer, preferably the same day. Muslims consider this a final service that they can do for their relatives and an opportunity to remember that their own existence here on earth is brief.
They laid so much emphasis on the belief in life after death that even a slight doubt in it meant denying God and made all other beliefs meaningless.