Kutiba AAalaykum itha hadara ahadakumu almawtu in taraka khayran alwasiyyatu lilwalidayni wal-aqrabeena (surah Baqarah: 180)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(2:180) It has been prescribed for you that when death approaches one of you and he is leaving some property behind him, he should bequeath it equitably for his parents and relatives : it is an obligation on those who fear AIIah. *182

Kutiba `alaikum izaa hadara ahadakumul mawtu in taraka khairanil wasiyyatu lilwaalidaini wal aqrabeena bilma`roofi haqqan `alalmut taqeen

*182). This injunction relates to a period of time when no rules had been laid down for the distribution of inheritance. Thus everyone was required to make testamentary disposal of their property so as to ensure that no disputes arose in the family and no legitimate claimant to inheritance was deprived of his due share. Later when God revealed a set of laws regarding the distribution of inheritance (see Qur'an 4: 11 ff.), the Prophet elucidated further the laws relating to testamentary disposition and inheritance by expounding two rules.
First, that no person can make any will regarding his estate in favour of any of his legal heirs. Their portions were laid down in the Qur'an and neither increase nor decrease in this was permissible, nor could any heir be disinherited, nor anything willed in favour of any heir over and above his legal portion. (See the Tradition: 'There may be no will in favour of the heir.' See Abu Da'ud, 'Al-Wasaya', 6; Tirmidhi, 'Al-Wasaya', 5; Nasa'i, 'Al-Wasaya', 5; Ibn Majah, 'Al-Wasaya', 5 - Ed.)
Second, that testamentary disposition might be made to the extent of one third of the estate, but no more. (See Bukhari, 'Al-Wasaya', 2 and 3; Muslim, 'Al-Wasiyah', 5-10; Abu Da'ud, 'Al-Wasaya', 2 - Ed.)
The purpose underlying these explanatory directives of the Prophet seems to be that at least two-thirds of the estate should be left aside to be distributed among the legal heirs according to the Qur'anic rules, and that a will could be made in respect of the whole or part of the remaining one-third. This could be made in favour of either relatives, whether close or distant, who are not legal heirs, or others not related by the blood-tie but who are deserving of assistance. Likewise, a will could be made in favour of charitable causes which are found worthy of support.
In later times people began to regard this directive regarding testamentary disposal as a recommendation only. The result was that this rule fell largely into disuse. It is significant, however, that the Qur'an mentions it as 'an obligation on the God-fearing'. Were Muslims to make this injunction an operative institution no trace would remain of the problems which agitate their minds respecting the Islamic law of inheritance , for example grandchildren whose parents had predeceased their paternal or maternal grandparents and who, under Islamic law, were not entitled to inherit from their grandparents. (The author suggests that re-activating the Qur'anic directive on testamentary disposal is the answer to this and similar problems - Ed.)