[Ruling on Bequest to Some of the Children]

Answer – and Allah is the One who grants success: Allah, exalted is He, has already made a bequest concerning the children, and has clarified His bequest to them; so it is not permissible to transgress the bequest of Allah, exalted is He, and to oppose it. He, exalted, said: "Allah instructs you concerning your children: for the male is like the share of two females", then He said at the end of that: "An obligation from Allah. Indeed, Allah is ever Knowing, Wise" [al-Nisāʾ:11]. So Allah, exalted is He, has informed that He has prescribed that as a prescription and has made it obligatory as an obligation, and that this prescription issues from the requirement of knowledge and wisdom.
Furthermore, bequest was obligatory before the revelation of the verses of inheritance in Sūrat al-Nisāʾ. Allah, exalted is He, said: "Prescribed for you, when death approaches any of you, if he leaves wealth, is that he should make a bequest for the parents and close relatives" [al-Baqarah:180]. Then, when the verses of inheritance in Sūrat al-Nisāʾ were revealed, the Prophet (may Allah bless him and his family and grant them peace) said: “Indeed Allah has given every one entitled [to a right] his right, so there is no bequest to an heir.”
Yes, if one of the children has a large family, and is poor and in need, while the rest of the children are in a better situation than him, and the father wishes to bequeath something to this poor child because of his poverty and need – then there is no objection to that.
Likewise, if one of the children shows much kindness and good treatment toward his father, unlike the rest of the children, and the like of that – then this is permissible and constitutes a specific [exception].
The proof of that is His, exalted is He, saying: "Or feeding, on a day of severe hunger, an orphan of near kin" [al-Balad:14–15], and His, exalted is He, saying: "Is there any reward for good other than good?" [al-Raḥmān:60]. And even if no evidence had come regarding that from the Sharīʿah, the intellect would itself have specified such cases.
Yes, and there is no contradiction between what we have mentioned and the hadith: “There is no bequest to an heir”; for what is meant by the hadith is the negation of the bequest that had been obligatory in the beginning of Islam. When the verses of inheritance were revealed, they abrogated it, so the Prophet (may Allah bless him and his family and grant them peace) said: “There is no bequest to an heir,” meaning that the bequest which had been obligatory upon you and prescribed for you – its obligation has been lifted, so it is not obligatory nor prescribed upon you. What is not meant by that is the negation of validity, which is the closer apparent meaning, because the indications of context show that what is meant is the negation of obligation, and this is not hidden from one who reflects.
Moreover, among what may support what we have mentioned is that it is established in the narration that Allah, exalted is He, has made for a person one-third of his wealth at the end of his life with which he may dispose by bequest and by drawing near to Allah with it in whatever avenues of righteousness he wishes; and the people with the greatest claim to righteousness and to drawing near to Allah through righteousness toward them are those who are closest, then those who are next closest.
If it is said: It is narrated from the Prophet (may Allah bless him and his family and grant them peace): “Fear Allah and treat your children equally.”
We say: [The hadith is] specific to what we have mentioned. Also, the one who gives his children, each according to his need, is not contradicting equality; for the one who spends on his young and his adult children, and clothes them both, is equal between them, even if the adult needs many times what the young one needs, in terms of larger garments and greater food.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2