إحكام الدّين من التحريف
Fortifying the Religion from Distortion
It is the duty of all Muslims, and in particular, the ‘ulamā, the scholars of Islam, to ensure that Islam retains its pristine nature and is protected from being distorted (taḥrīf). Especially in an age where we are witnessing a small group of individuals using Islam for their own personal motives. Among the many causes of distortion in the religion are the following:
Being lax with matters such as prayers and education will lead to successive generations ultimately neglecting them. The teaching of religion and acting upon knowledge will become extinct, and enjoining good and forbidding evil will cease. Before long, customs will emerge that oppose the religion and the nature of people will conflict with the demand of the divine law. Eventually, a time will come where nothing of the religion will remain. The cause of such laxity is to be found in a number of things:
عدم تحمل الرِّوَايَة عَن صَاحب الْملَّة وَالْعَمَل بِهِ
The absence or lack of regard of transmitting from the founder of the religion (i.e. the Prophet, may the peace and blessings of God be upon him) and [failing] to act upon it. In essence, refusing to accept the proof of the prophetic traditions or taking them as a means of guidance for the conduct of our daily affairs.
الْأَغْرَاض الْفَاسِدَة الحاملة على التّأْوِيل الْبَاطِل
Corrupt intentions which lead to distorted and false exegesis and interpretations. This can stem from untrained individuals of the sacred sciences providing false exegesis to please leaders or trying to fit the divine law to suit modern concerns.
شيوع الْمُنْكَرَات وَترك عُلَمَائهمْ النَّهْي عَنْهَا
The spreading of evil acts and the scholars’ failure to forbid them. It is obligatory for scholars to remain firm in speaking the truth and standing up for justice.
In essence, this occurs when the ruling of something that is ordered or forbidden is overextended to another ruling that resembles the original ruling in certain ways or where a certain part of the ‘illah (reason for the legislation) is found. It can also occur when this ruling is overextended to some of its anticipated sources or motives. Thus, the following can occur:
وَكلما اشْتبهَ عَلَيْهِ الْأَمر لتعارض الرِّوَايَات الْتزم الأشد، ويجعله وَاجِبا
When something is ambiguous due to a conflict with the traditions of the Prophet, holding firm to the most stringent view and making it obligatory.
وَيحمل كل مَا فعله النَّبِي صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ على الْعِبَادَة، وَالْحق أَنه فعل أَشْيَاء على الْعَادة
To take everything that the Prophet did as an act of worship though the truth is that he did certain things according to the custom of his time. 
Being excessively strict
This occurs when acts of worship are pursued which the law-giver did not command, such as continuously fasting, praying the entire night, to remain celibate, to disengage from the world, and making recommended acts as something that is compulsory. Thus, you have the saying of the Prophet, may the peace and blessings of God be upon him:
لن يشاد الدّين أحد إِلَّا غَلبه
‘No one makes religion too strict but that is overwhelms him.’ 
Preference (istiḥsān) 
فيختلس من أسرار التشريع، فيشرع للنَّاس حَسْبَمَا عقل من الْمصلحَة
This occurs when certain inner meanings of the law are appropriated by [ignorant] people according to what they think is the beneficial purpose. As an example, the Jews believed that the Law-Giver only commanded punishments (ḥudūd) as a deterrent and a mechanism for reforming society (i.e. not to be actually applied) so they considered stoning as an act that leads to dispute and hence something that would lead to a worse outcome. Therefore, they applied the principle of preference in sanctioning the blackening of the face and skin (of an adulterer) with coal instead.
Ibn Sīrīn says:
أول من قَاس إِبْلِيس، وَمَا عبدت الشَّمْس وَالْقَمَر إِلَّا بالمقاييس
‘The first one to apply analogy was Iblīs and the worship of the moon and sun only came about through analogy.’
And from al-Ḥasan (al-Baṣrī) that he recited the following from the Qur’ān:
خلقتني من نَار وخلقته من طين
‘You created me fire and You created him from earth.’
and he then went on to say:
قَاس إِبْلِيس وَهُوَ أول من قَاس
‘Iblīs used an analogy and he was the first to use an analogy’ 
The crux of the matter here, and this is important, is that the istiḥsān of the ignorant ones is blameworthy, and not the istiḥsān of scholars of law, since this type analogy, is a proof in the religion.
Following consensus (ijmā’) without any basis
وَذَلِكَ فِيمَا لَيْسَ لَهُ أصل من الْكتاب وَالسّنة، وَهَذَا غير الْإِجْمَاع الَّذِي اجْتمعت الْأمة عَلَيْهِ فَإِنَّهُم اتَّفقُوا على القَوْل بِالْإِجْمَاع الَّذِي مُسْتَنده الْكتاب وَالسّنة أَو الاستنباط من أَحدهمَا
This occurs when consensus is declared on issues that do not find their basis in the Qur’ān and Sunnah. This is not the consensus which the community has agreed upon, since consensus is agreed upon when it is founded upon the Qur’ān and sunna, or is directly derived from one of them. For Allāh says:
وَإِذَا قِيلَ لَهُمُ اتَّبِعُوا مَا أَنزَلَ اللَّهُ قَالُوا بَلْ نَتَّبِعُ مَا أَلْفَيْنَا عَلَيْهِ آبَاءَنَا ۗ
‘When it is said unto them, “follow what God has sent down,” they say, “Nay, we follow that which we found our fathers doing.”
This often occurs when people claim consensus of their forefathers whilst remaining ignorant of the Qur’ān and sunnah. This is was what led to the Jews denying the prophethood of Jesus and Muḥammad, may peace and blessings of God be upon them; because they [blindly] followed their ancestors.
To [blindly] follow the legal decisions of someone who is not entirely fallible i.e. someone other than a Prophet
تَقْلِيد غير الْمَعْصُوم أَعنِي غير النَّبِي الَّذِي ثبتَتْ عصمته، وَحَقِيقَته أَن يجْتَهد وَاحِد من عُلَمَاء الْأمة فِي مَسْأَلَة، فيظن متبعوه أَنه على الْإِصَابَة قطعا أَو غَالِبا، فيردوا بِهِ حَدِيثا صَحِيح
This occurs when someone other than a Prophet (whose infallibility is established) – a learned scholar – uses independent reasoning (ijtihād) and his followers assume that his answer is absolutely correct or correct in most cases, and thus, they reject a sound ḥadīth.
إِنَّهُم اتَّفقُوا على جَوَاز التَّقْلِيد للمجتهدين مَعَ الْعلم بِأَن الْمُجْتَهد يُخطئ، ويصيب، وَمَعَ الاستشراف لنَصّ النَّبِي صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ فِي الْمَسْأَلَة والعزم على أَنه إِذا ظهر حَدِيث صَحِيح خلاف مَا قلد فِيهِ ترك التَّقْلِيد، وَاتبع الحَدِيث
This type of taqlīd is different from the one the rightly guided community has agreed upon, since it is agreed that taqlīd is permissible in following scholars of independent reasoning (mujtahidūn) whilst recognising that they may err or be correct, and if a reliable ḥadīth comes which opposes them, then taqlīd in this instance should be abandoned and the ḥadīth followed. 
The Prophet, may peace and blessings be upon him, stated in relation to the verse:
اتَّخَذُوا أَحْبَارَهُمْ وَرُهْبَانَهُمْ أَرْبَابًا مِّن دُونِ اللَّهِ وَالْمَسِيحَ ابْنَ مَرْيَمَ وَمَا أُمِرُوا إِلَّا لِيَعْبُدُوا إلَاهًا وَاحِدًا ۖ لَّا إِلَٰهَ إِلَّا هُوَ ۚ سُبْحَانَهُ عَمَّا يُشْرِكُونَ
‘They have taken their rabbis and monks as lords apart from God, as well as the Messiah, son of Mary, though they were only commanded to worship one God. There is no God but he! Glory be to Him above the partners they ascribe.’
إِنَّهُم لم يَكُونُوا يَعْبُدُونَهُمْ، وَلَكنهُمْ كَانُوا إِذا أحلُّوا لَهُم شَيْئا اسْتَحَلُّوهُ، وَإِذا حرمُوا عَلَيْهِم شَيْئا حرمُوهُ
‘That is was not that they used to worship them, but rather if they said that a thing was permitted to people, then they would take it as such, and that if they forbade them something, then they would take it to be forbidden.’ 
Mixing one religion with another
خلط مِلَّة بِملَّة حَتَّى لَا تتَمَيَّز وَاحِدَة من الْأُخْرَى، وَذَلِكَ أَن يكون إِنْسَان فِي دين من الْأَدْيَان تعلق بِقَلْبِه عُلُوم تِلْكَ الطَّبَقَة، ثمَّ يدْخل فِي الْملَّة الإسلامية، قيبقى ميل قلبه إِلَى مَا تعلق بِهِ من قبل لَمْ يَزَلْ أَمْرُ بَنِي إِسْرَائِيلَ مُعْتَدِلاً حَتَّى نَشَأَ فِيهِمُ الْمُوَلَّدُونَ أَبْنَاءُ سَبَايَا الأُمَمِ فَقَالُوا بِالرَّأْىِ فَضَلُّوا وَأَضَلُّوا
This occurs when a person enters Islam but maintains some form of emotional attachment to what they believed in before. So much so that they will seek methods to make room for what they had before to bring it into Islam. Thus, we have the Prophet, may the peace and blessings of God be upon him, saying:
لَمْ يَزَلْ أَمْرُ بَنِي إِسْرَائِيلَ مُعْتَدِلاً حَتَّى نَشَأَ فِيهِمُ الْمُوَلَّدُونَ أَبْنَاءُ سَبَايَا الأُمَمِ فَقَالُوا بِالرَّأْىِ فَضَلُّوا وَأَضَلُّوا
‘The situation of the Children of Israel was balanced until there rose among them those of mixed descent and the children of prisoners of (other) nations so they spoke on the basis of their own opinions and went astray and led others astray.’
وَمِمَّا دخل فِي ديننَا عُلُوم بني إِسْرَائِيل وتذكير خطباء الْجَاهِلِيَّة وَحِكْمَة اليونانيين ودعوة البابليين وتاريخ الفارسيين والنجوم والرمل وَالْكَلَام
Among other things which have become interpolated in our religion are the canons of the Children of Israel, the exhortations of sermons of the age of ignorance, Greek sciences, propaganda of the Babylonians, history of the Persians, astrology, geomancy, and rationalist theology.
And only Allah knows best.
 As the Qur’ān, for example, states, ‘Then they were succeeded by a generation who neglected prayer and followed based desires’ (19:59).
 For example, by not eating or engaging in sexual intercourse before dawn because the law giver intended by fasting to subdue the lower self.
 For example, making it forbidden to kiss one’s spouse when fasting based on the view that it induces sexual intercourse or that it is similar to it. Though it is obviously not and the Prophet corrected this misunderstanding in this case.
 For example, to make ablution compulsory for that which has touched the fire.
 For example, the dietary preferences of the Prophet.
 Al-Bukhārī and Nasā’ī. The Prophet, may the peace and blessings of God be upon him, said, ‘Religion is very easy and whoever overburdens himself in his religion will not be able to continue in that way. So you should not be extremists, but try to be near to perfection and receive the good tidings that you will be rewarded; and gain strength by worshipping in the mornings, the afternoons, and during the last hours of the night.’
 This is not referring to juristic preference as understood and practiced by scholars of Islamic legal theory since this is legitimate deviation from qiyās in which a discretionary interpretation is used more freely with the goal of being a ruling for the public interest. Here, however, we are referring to the preference practiced by those not versed in legal theory.
 References (including subsequent ones) can be found in al-Dārimī, bāb taghayyur al-zamān wamā yaḥduthu fīhī. (the changing of the age and what changes in it).
 Qur’ān, 2:170.
 Though this is not a straightforward matter as it requires a number of options and processes to be followed by those trained in the sacred sciences.
 Qur’ān 9:31
 Ibn Mājah.