﴿ ذَٰلِكَ وَمَن يُعَظِّمْ حُرُمَٰتِ ٱللَّهِ فَهُوَ خَيْرٌۭ لَّهُۥ عِندَ رَبِّهِۦ ۗ وَأُحِلَّتْ لَكُمُ ٱلْأَنْعَٰمُ إِلَّا مَا يُتْلَىٰ عَلَيْكُمْ ۖ فَٱجْتَنِبُوا۟ ٱلرِّجْسَ مِنَ ٱلْأَوْثَٰنِ وَٱجْتَنِبُوا۟ قَوْلَ ٱلزُّورِ ﴾

“All this [is ordained by God]; and if one houours God’s sacred commandments, it will redound to his own good in his Sustainer’s sight. And all [kinds of] cattle have been made lawful to you [for sacrifice and food], save what is mentioned to you [as forbidden]. Shun, then, [all that God has forbidden and, most of all,] the loathsome evil of idolatrous beliefs and practices; and shun every word that is untrue,”

What is permitted (halal) and what is prohibited (haram); what is sacred and what is not; which way of worship are proper and which improper—all these matters have been made absolutely clear by God through His prophets. Any changes in these matters are not permissible. Any change made in these things is highly wrong, in the eyes of God. Therefore, it is necessary for man to follow the Prophet’s instructions. He should in no case increase or decrease what is prescribed by the Prophet. These are matters the reality of which is known only to God. When a man on his own says something on this subject, he virtually claims, in effect, to have knowledge about things of which he has no knowledge. Obviously, what wrong can be greater than this.