“Verily, he who has purified the heart is successful and he who has despoiled it has lost.”
Tasawwuf is the effort to purity the heart from the lowly bestial attributes of lust, calamities of the tongue, anger, malice, jealousy, love of the world, love of fame, niggardliness, greed, ostentation, vanity, deception, etc. At the same time it aims at the adornment of the heart with the lofty attributes of repentance, perseverance, gratefulness, fear of Allah, hope, abstention, tauheed, trust, love, sincerity, truth, contemplation, etc.
The department of the Shariah relating to external deeds like salat and zakat is called fiqh while the one dealing with the internal affairs and states of the heart is called tasawwuf. Both are commanded in the Qur’an and Hadith. Thus while commanding Salat and Zakat, the Qur’an also commands gratefulness and love of Allah and condemns the evil of pride and vanity. These commands are as much a mandatory requirement as the ones dealing with external deeds.
A lot of people have misunderstandings about tasawwuf. Many think that it is something beyond Qur’an and Sunnah. Errant Sufis as well as the superficial ulema, although on the opposite ends of the spectrum, are together in holding this mistaken notion. Consequently the first group has shunned the Qur’an and Hadith while the second group has shunned tasawwuf. Actually, although the term tasawwuf, like many other religious terms in use today, evolved later, the discipline is very much part of the Shariah.