It is true that a Muslim should not let even three nights pass by without having his will prepared if he has something in his possession.
The will is a testament and advice for the heirs of the person.
One should include in the testament the following:
1- An advice to the heirs, reminding them to remain mindful of their duties towards Allah and fellow human being and to remain steadfast on the path of righteousness.
2- To follow the Sunnah of the Holy Prophet Sallallahu Alaihe Wa Sallam.
3- To perform all the burial and funeral procedures in accordance with the Sunnah of the Prophet Sallallahu Alaihe Wa Sallam.
4- To payoff any debts that remain unpaid before the distribution of heritage.
5- To To payoff any contributions that were promised during the life of deceased.
6- To distribute the wealth in accordance with the Islamic law of inheritance.
The above things should essentially be included in the Wasiya (testament). One may add other item to the list as well that one feels necessary to be addressed.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America
8 Rabiul Awwal 1432/ February 12 2011