Will writing has been known in the conventional financial planning as bequeath or arrangement, by making will, to give wealth to some body when one dies. Nowadays, there are industries or companies that provide this kind of services. Will in Islam is known as wasiyyah. It is very significant means to provide a flexible instrument in estate planning in Islam. Wassiyyah basically means one gives a gift to others in term of wealth, debt and beneficence of one's property after his death. It depicts the differences between wassiyah and hibah. Unlike hibah, wassiyyah is a gift, which only executed after the death of the giver. Hibah is a gift only in the form of property, while wasiyyah may be in the form of property, debt or beneficence.

It has been recommended by the qur'an and hadith as well as practiced by the prophet's companions in their time. As God says in qur'an "It is prescribed, when death approaches any of you, if he leaves any goods that he makes a bequest to parents and next of kin, according to reasonable usage; this is due from the God-fearing" (Qur'an 2:180). In another verse, God says "Those of you who die and leave widows should bequeath for their widows a year's maintenance and residence; but if they leave (the residence) , there is no blame on you for what they do with themselves, provided it is reasonable, and God is exalted in power, wise" (Qur'an 2:240).

From the above verses, it is clear that making will or bequest is an obligatory for all Muslims before they pass away. Muslim Scholars are in the opinions that these verses were revealed before verses on the laws of heritance and thus it were abrogated by Qur'an 4:11-12 and 186. However, this does not mean that there is no need to write bequest. In fact, Islam encourages its adherents to make last will and bequest before any one of Muslims die. This is evident in the hadith narrated by Bukhari and Muslim from Ibn Umar , the prophet says "there is not right for any Muslim person who has anything to bequeth that he may pass even two nights without having his will written" and Ibn Majjah narrated from Jabir that the prophet says "Those who die leaving a will, he dies in the path of the truth and righteousness, dies in obedience and faith, dies receiving forgiveness".

In addition the companions of the prophet peace be upon him used to write will to give certain portion of their property in order to move themselves closer to God. However writing will or bequest in Islam is very dynamic in the sense it may become Wajib (obligatory), Mandub (supererogatory), Haram (unlawful), Makruh (hateful), Mubah (permissible). It becomes an obligatory if it is related to the debt and the right of God such as property, which is not yet spent for payment of debt or zakat. At the same time it may be supererogatory if it is related to giving certain portion of the estate for needy members of family who are not entitled to get the inheritance. This category will be useful for estate distribution as a complementary device to faraid, the Islamic laws of inheritance.

Wassiyyah may become unlawful if it leads to the harm of heirs. It was narrated by Nasa'i for instance the will may not valid (unlawful) if the deceased gives his portion of property for sinful deeds such as related to alcohols, gambling and the like. At the same time it become hateful if the will is written while the heirs are in need to the wealth. Finally it may be permissible if the will written in order to enrich certain member of family who are already rich.

The bequest however must not exceed the maximum limit which was prescribed by the prophet peace be upon him; as once the prophet visited Sa'ad ibn Abi Waqas, he was asked to give permission to allow him to give all his property as the bequest. The prophet replied no, then half of it, then prophet said no, then Sa'ad said how about one third, the prophet said, "one third and one third is too much. Indeed if you left the heirs rich is better then you left them poor…". Islam in fact does not allow Muslims to write the bequest or make will for the eligible heirs. If that happens it is not valid unless the other eligible heirs agree to it. The prophet highlighted it once he said "God has given each of the heirs their portion of the estate, so there should not be any more bequeaths for them".

In conclusion, the will that is encouraged by the prophet is not inconsistent with the rules laid down by the Qur'an. As it is known, the Islamic law of inheritance sets prescribed limits but allows the instrument of wassiyyat as a flexible way to distribute one's wealth according to his desires. For instance, if the deceased left his son who is not entitled to get the estate for being different religion, the father may make will or bequest up to one third of his wealth to be given to his non-Muslim son before he dies. However this flexibility does not necessarily mean that one is allowed unlimited freedom to decide as he wishes. As a result, Islamic financial planners should be careful in rendering the advice to the client with regard to estate planning, so that the client will do justly in his last will, as narrated by Abd al-Razaq from Abi Hurayrah, the prophet peace be upon him says, "a man may do good deeds for 70 years but if he acts unjustly when he leaves his last will, the wickedness of his deed will be sealed upon him, and he will go to hell And if (on the other hand) a man acts wickedly for 70 years but is just in his last will, the goodness of his deed will be sealed upon him and he will enter the paradise".