Tasawwuf is a system of discipline which teaches ways of finding peace by introducing the heart to Allah and thereby attaining peace..
Dīn is a system of tarbiya that addresses both the inner and the outer states of people, comprising divine adab and laws, whereby a person may attain happiness in both worlds. This tarbiya occurs in three basic areas. The first is belief, the second is ibādat (worshipping) and the third is morals. The dīn starts with believing and is experienced through ibādat and tā’at. Through adab, good morals, divine love, cleansing the heart, giving tarbiya (taming) the nafs, one proves the friendship to Allāh and attains the joy of being one of His good servants. So, being a kāmil (perfect; thrived or genuine) mu’min depends on living dīn in a kāmil way.
This well-known hadīs-i sharīf explains the concept of the dīn as based on these three basic principles.
One day the messenger of Allāh (SAW) was sitting with the sahāba-i kirām (honourable companions; companions of Rasūlullāh) in the mosque (Masjid-i Nabawī). At that moment a man appeared. The man was dressed in white; his hair was black and his scent pleasant, he bore no trace of a tarvel and nobody knew him. He entered the presence of the beloved prophet (SAW) and sat in the very front of him, put his hands on his knees and started to ask questions. Firstly: “O Muhammad, can you tell me what is Islām?”
Rasūlullāh (SAW) replied:
“Islām is to believe there is no god but Allāh and bearing witness that Muhammad is His messenger, as well as performing salāt (prayer), giving zakāt, fasting, visiting Allāh’s house (Ka’bah) and doing hajj, if you are able to do so.”
”Can you tell me what the īmān is?” asked the man:
Rasūlullāh (SAW) said:
“Īmān is believing in Allāh, His angels, His books, His prophets and the day of judgment, and that all things good and bad occur with Allāh’s doing.”
Again the person asked, “What is ihsān? Can you tell me about ihsān?”.
Rasūlullāh (SAW) said:
“ihsān means to worship Allāh as if you see Him. Even though you cannot see Him, He sees you,” he said.
The person asked:
“Can you tell me when the end of the world will be?”
Rasūlullāh (SAW) said:
“The person who is asked about this subject, is no more informed than the one who is asking.”
But he gave information about some of the signs for the qiyāmat (the end of the world). The person who asked these questions asked permission to stand up and suddenly disappeared from sight. A little later, the beloved messenger of Allāh (SAW) said:
“Find and bring the person who asked the questions”
The companions looked for him but could not find him. Rasūlullāh (SAW) said:
“He was Jabrā’īl (AS – alayhissalām), and he came to you to teach you your dīn.” 
This means that Jabrā’īl (AS) came not to learn for himself, but to teach the dīn to people this way. Almighty Allāh sent him to the Prophet (SAW) to teach the essence of the dīn and to grant the honourable companions the honour of seeing him.
As related in this hadīs, dīn is constructed upon three foundations. These are īmān , ibādat and ahlāq (morals).
Īmān is the basis of belief. It is studied by kalām ālims (quranic scholars). Fiqh ālims (scholars of islamic law) study ibādats. Ahlāq (morals), on the other hand, is a person’s inner tarbiya. It involves the removing of a person’s bad attributes and replacing them with good ones. This kind of tarbiya is best carried out under the nazar (ma’nawī gaze) and supervision of kāmil persons who have been guided in this field. These kāmil people are generally trained under the supervision of a murshid, in tasawwuf schools founded on the principles of Qur’ān and Sunnat.
As it is mentioned in the hadīs-i sharīf, ihsān is the foundation of tasawwuf tarbiya, the basic goal of which is spiritual purification and beauty.
Just as true īmān and decent ibādat is farz (an obligation) upon every mu’min, purifying the heart, disciplining the nafs and acquiring ahlāq is an obligation, too. Anything which facilitates or enables the performance of a farz is just as important as the farz itself.
No mu’min should say “I have īmān and I perform ibādats, but I do not need ihlās, divine love and ma’rifatullāh (knowledge of Allāh). I do not need cleansing of the heart; I cannot be bothered with disciplining the nafs.” A person with this attitude is lacking, and he can neither know his dīn nor live it properly. Anybody whose heart does not find peace with almighty Allāh is deprived. Eternal peace has been connected to divine love and zikrullāh (zikr of Allāh). This definite rule, which is never going to change, is told in Qur’ān, in the following āyat:
وَيَقُولُ الَّذِينَ كَفَرُواْ لَوْلاَ أُنزِلَ عَلَيْهِ آيَةٌ مِّن رَّبِّهِ قُلْ إِنَّ اللّهَ يُضِلُّ مَن يَشَاء وَيَهْدِي إِلَيْهِ مَنْ أَنَابَ
“(Allāh) guides to Himself those who repent and have faith; whose hearts find comfort in the zikr of Allāh. Surely in the zikr of Allāh all hearts are comforted.” [Ra’d 13:27-28]
الَّذِينَ آمَنُواْ وَتَطْمَئِنُّ قُلُوبُهُم بِذِكْرِ اللّهِ أَلاَ بِذِكْرِ اللّهِ تَطْمَئِنُّ الْقُلُوبُ
As you can see, tasawwuf is a system of tarbiya which teaches ways of finding peace by introducing the heart to Allāh and thereby attaining peace; it also enables the realizātīon of this. Tasawwuf is a school of ahlāq. Purification of the heart and good morals are the internal fiqh of the dīn. Qur’ān calls this as “taqwā”. The struggle to attain taqwā is known as tazkiyah (purification). Tazkiyah means cleansing the heart from the filth of denial, shirk (worshiping any other than Allāh), rebellion and ghaflat; to purify the soul, to save the nafs from bad habits and to adorn it with good traits. The goal in all this is the attainment of Allāh’s rizā and His friendship. Surely all the methods and ādāb of a tarbiya that aims for Allāh’s rizā should be in similar accordance with Allāh’s rizā.
Allāh Ta’ālā has placed His messenger, the beloved Rasūlullāh (SAW) at the centre of divine tarbiya and His friendship. Nobody can reach Allāh and His friendship without obeying him.
Allāh Ta’ālā presented all mankind with this divine guideline:
قُلْ إِن كُنتُمْ تُحِبُّونَ اللّهَ فَاتَّبِعُونِي يُحْبِبْكُمُ اللّهُ وَيَغْفِرْ لَكُمْ ذُنُوبَكُمْ وَاللّهُ غَفُورٌ رَّحِيمٌ
“Say, (O Muhammad, to mankind): If you love Allāh, follow me; Allāh will love you and forgive you your sins. Allāh is Ghafūr and Rahīm (forgiving and merciful).” [Al- Imran 3:31]
As it is explained by ālims, the word “following” mentioned in this āyat is no ordinary following. It includes sincere love for our beloved prophet (SAW). This love requires following Rasūlullāh (SAW) with full taslīmiyat, with the heart, tongue, in essence and words, with any state, and morals. When a mu’min adheres tightly to the way of Sunnat inwardly and outwardly, with his beliefs and his lifestyle, and does so until he dies, he will have carried out his duty of obedience to Allāh and gained the love of Allāh.
Rasūlullāh (SAW) taught and demonstrated the dīn to the ashāb-i kirām (RA: radiyallāhu anhum- May Allāh be pleased with them) in the form of īmān, worshipping and ihsān, and then he honoured the āhirat (passed away).
The sahāba-i kirām (RA) transmitted the dīn, the state of īmān, ibādat and ihsān in their entirety to the people who came after them. Islām was taken into consideration as a whole by the first two generations. They tried to preserve the external and internal ways of the dīn with equal care. Then, the situation changed.
In Tabarani’s account the ending goes “The belief that everything, good and bad, sweet and bitter, comes from Allah.” (see Tabarani, al-Kabir nr. 13582; Heysemî, ez-Zevâid, 1/41).
 Bukhârî, Iman, 37; Müslim, Iman, 1; Abû Davud, Sunnah, 16; Tirmidhî, Iman, 4; Ibn Mâje, Mukaddime, 9; Ahmed, Müsned, 1/52.[/box]