The Islamic Personality by Sheikh Taqīuddīn An-Nabahānī

Linguistically, ‘aqīdah (creed) means

The matter on which the heart has tied a knot (belived in firmly). The meaning of tying a knot is to be sure of, that is, believe in it decisively, this is general, which includes belief in everything. However, the belief in a certain matter is examined in terms of the thing in which the conviction has taken place. If it was a fundamental matter or one that is branching out from a fundamental matter then it is correct to call it an ‘aqīdah (creed) and it is correct for one to take it as a fundamental criterion for other beliefs, so the heart tying a knot on it will have a manifest impact. If the matter in which one has conviction is not a fundamental matter or is branching out from a fundamental matter then it will not be part of the ‘aqīdah (creed), this is because the heart tying a knot on it will not have a manifest impact. In believing in it one will not find in it any reality or any benefit. And when the heart's tying a knot on any subject matter has an effect, it will push him to determine his stance towards it in terms of belief and denial, and then it will be part of the ‘aqīdah (creed).

The ‘aqīdah (creed) is a comprehensive thought concerning the universe, man and life, what preceded this wordly life and what is to follow it, and the relationship of this life with what preceded it and what is to follow it. This is the definition of every ‘aqīdah (creed) and it applies to the Islamic ‘aqīdah (creed). Included in it are the unseen matters. So the belief in Allah , His angels, His books, His Messengers, the Last Day, divine fate and destiny (qadā’ wal qadā’r), that good and bad is from Allah  is the Islamic ‘aqīdah (creed). The belief in Paradise (jannah), Hellfire (nar), angels, shaytan’s etc is from the Islamic ‘aqīdah (creed), thoughts and whatever relates to it. Also narrations and the unseen things that cannot be percieved are considered from ‘aqīdah (creed).

As for the Sharī’ah rules;

In other words they are thoughts regarding an action or the attributes of the human being as being part of his actions. Thus, leasing, selling, dealing with usury, custody, representation (wikala), prayer (salah), appointing a Khalifah, implementation of the punishments (Hudud) of Allah , the fact that the Khalifah should be a Muslim and the witness be just and the ruler be a man etc All of these are considered to be from the Sharī’ah rules. Oneness of Allah (Tawheed), The Message (Risalah), resurrection (ba'th), truthfulness of the Messenger, infallibility of the Prophets, that fact that the Qur’ān is Allah's speech (kalam), reckoning (hisab) and torment ('azaab) etc, all of these are considered part of the ‘aqīdah (creed). Thus, the articles of belief (‘aqa’id) are thoughts that are believed. And the Sharī’ah rules are the address which relates to the action of the human being. Thus, the two rakats of fajr is a Sharī’ah rule in terms of praying them. And the belief that they are from Allah  constitutes ‘aqīdah (creed). So praying the two rakats Sunnah of fajr is Sunnah. If one does not pray it he is not blamed. If he prays it he will get the reward like the two rakats (Sunnah) of Maghrib prayer, both of which are the same in terms of the Sharī’ah rule. As for in terms of the ‘aqīdah (creed), belief in the two rakats of fajr is a definite matter, rejecting them is disbelief (kufr) because they have been proven by way of tawatur (recurrent lines of transmission). As for belief in the two rakats of Maghrib, it is requested but if one rejects them it is not considered kufr because they have been proven by speculative (zanni)

evidence which is a solitary report (khabar al-ahad). The solitary report (khabar al-ahad) is not a proof in the articles of belief ('aqaid). Cutting the hand of the thief is a Sharī’ah rule but the fact that it is from Allah  and believing in it is from the 'Aqeeda. The prohibition of usury is a Sharī’ah rule. But, believing that it is rule from Allah  is part of the 'Aqeeda etc.

Therefore, there is a difference between the ‘aqīdah (creed) and the Sharī’ah rule. ‘aqīdah (creed) is Imān, which is the definite belief which is in agreement with the reality based on evidence. In this decisiveness and certainty is required. The Sharī’ah rule is the address of the Legislator pertaining to the actions of the servants. In this speculative knowledge (zann) is sufficient. Thus, comprehension of the thought and the belief in whether it has a reality or not is part of the ‘aqīdah (creed) and the comprehension of a thought and considering it or not considering it as a solution for an action of a human being is a Sharī’ah rule. In order to consider the thought as a solution the speculative (zanni) evidence is sufficient. However, in order to believe in the presence of a reality of a thought, one must have definite evidence (dalīl qat'i).