Meaning, the Fara'id are Allah's set limits. This includes what Allah has alloted for the heirs, according to the degree of relation they have to the deceased, and their degree of dependency on him. Therefore, do not transgress or violate them. So Allah said;
وَمَن يُطِعِ اللَّهَ وَرَسُولَهُ
(And whosoever obeys Allah and His Messenger,) regarding the inheritance, and does not add or decrease any of these fixed shares by use of tricks and plots. Rather, he gives each his appointed share as Allah commanded, ordained and decided,
تِلْكَ حُدُودُ اللَّهِ وَمَن يُطِعِ اللَّهَ وَرَسُولَهُ يُدْخِلْهُ جَنَّـتٍ تَجْرِى مِن تَحْتِهَا الاٌّنْهَـرُ خَـلِدِينَ فِيهَا وَذلِكَ الْفَوْزُ الْعَظِيمُ - وَمَن يَعْصِ اللَّهَ وَرَسُولَهُ وَيَتَعَدَّ حُدُودَهُ يُدْخِلْهُ نَاراً خَـلِداً فِيهَا وَلَهُ عَذَابٌ مُّهِينٌ
(Will be admitted to Gardens under which rivers flow (in Paradise), to abide therein, and is the great success. And whosoever disobeys Allah and His Messenger, and transgresses His (set) limits, He will cast him into the Fire, to abide therein; and he shall have a disgraceful torment.) This is because he changed what Allah has ordained and disputed with His judgment. Indeed, this is the behavior of those who do not agree with what Allah has decided and divided, and this is why Allah punishes them with humiliation in the eternal, painful torment. Imam Ahmad recorded that Abu Hurayrah said that, the Messenger of Allah ﷺ said,
«إِنَّ الرَّجُلَ لَيَعْمَلُ بِعَمَلِ أَهْلِ الْخَيْرِ سَبْعِينَ سَنَةً، فَإِذَا أَوْصَى حَافَ فِي وَصِيَّتِهِ، فَيُخْتَمُ لَهُ بِشَرِّ عَمَلِهِ، فَيَدْخُلُ النَّارَ، وَإِنَّ الرَّجُلَ لَيَعْمَلُ بِعَمَلِ أَهْلِ الشَّرِّ سَبْعِينَ سَنَةً، فَيَعْدِلُ فِي وَصِيَّتِهِ فَيُخْتَمُ لَهُ بِخَيْرِ عَمَلِهِ فَيَدْخُلُ الْجَنَّة»
(A man might perform the actions of righteous people for seventy years, but when it is time to compile his will, he commits injustice. So his final work will be his worst, and he thus enters the Fire. A man might perform the deeds of evil people for seventy years, yet he is fair in his will. So his final work will be his best, and he thus enters Paradise.) Abu Hurayrah said, "Read, if you will,
تِلْكَ حُدُودُ اللَّهِ
(These are the limits (set by) Allah) until,
عَذَابٌ مُّهِينٌ
(a disgraceful torment.)." In the chapter on injustice in the will, Abu Dawud recorded in his Sunan that Abu Hurayrah said that the Messenger of Allah ﷺ said,
«إِنَّ الرَّجُلَ لَيَعْمَلُ أَوِ الْمَرْأَةَ بِطَاعَةِ اللهِ سِتِّينَ سَنَةً، ثُمَّ يَحْضُرُهُمَا الْمَوْتُ، فَيُضَارَّانِ فِي الْوَصِيَّـةِ، فَتَجِبُ لَهُمَا النَّار»
(A man or a woman might perform actions in obedience to Allah for sixty years. Yet, when they are near death, they leave an unfair will and thus acquire the Fire.) Abu Hurayrah then recited the Ayah,
مِن بَعْدِ وَصِيَّةٍ يُوصَى بِهَآ أَوْ دَيْنٍ غَيْرَ مُضَآرٍّ
(After payment of legacies he (or she) may have bequeathed or debts, so that no loss is caused), until,
وَذلِكَ الْفَوْزُ الْعَظِيمُ
(and that is the great success.) This was also recorded by At-Tirmidhi and Ibn Majah, and At-Tirmidhi said, "Hasan Gharib".