Source: Haqeeqat-ut-Tasawwuf (pg. 11-15) [1422 1st Edition]
The words Tasawwuf and Soofiyyah were not known during the first generation of Islaam. Rather, they were only introduced into it after that or they were adopted into Islaam from other nations.
Shaikh-ul-Islaam Ibn Taimiyyah, may Allaah have mercy on him, said in Majmoo’-ul-Fataawaa: “As for the term Soofiyyah (Sufism), then it was not heard of during the first three generations of Islaam. Rather, speech concerning it only became known after the first three generations. Several Imaams and scholars spoke about it afterward, such as Imaam Ahmad bin Hanbal, Abu Sulaymaan Ad-Daaraanee and others. It was also reported from Sufyaan Ath-Thawree that he spoke about it. Some of them also mentioned that on the authority of Al-Hasan Al-Basree. They differed in their views on the meaning of what a Soofee ascribes himself to, since the word ‘Soofee’ is a noun indicating an ascription, such as Al-Qurshee, Al-Madanee and so on.
It is said to be an ascription to Ahlus-Suffah, but this is an error, since if this were the case, they would call themselves Suffee. It is also said to be an ascription to the saff (row) that is the foremost before Allaah, but this is also wrong, since if this were the case, they would call themselves Saffee. It is also said to be an ascription to the safwah (best) from Allaah’s creation. This too is an error, since if it were so, they would have to call themselves Safwee. It is also held to be an ascription to Soofah bin Bishr bin Udd bin Taabikhah, an Arab tribe that used to be located next to Makkah in the past, which the ascetics would ascribe themselves to. Even though the ascription of Soofee is in conformity to this person’s name (Soofah) from a grammatical standpoint, it is also a weak opinion, since these people were not well known to most of the ascetics and because if the ascetics were to ascribe to them, it would have been more likely that they would have ascribed to them during the era of the Sahaabah, Taabi’een and the Atbaa’ at-Taabi’een.
It is also due to the fact that the majority of those who speak on behalf of the Soofees are not aware of this tribe and they are not pleased with being attributed to a tribe from the Days of Ignorance (Jaahiliyyah), which did not exist during the era of Islaam. It is also held, and this is the most well known opinion, that Soofee is an ascription to soof (wool). This was since the first time that the Soofees appeared was in Basrah (‘Iraq).
The first people that established the role of Soofiyyah were some of the companions of ‘Abdul-Waahid bin Zayd. ‘Abdul-Waahid was one of the companions of Al-Hasan Al-Basree who lived in Basrah and was into such great lengths in abstinence (zuhd), worship (‘ibaadah), fear of Allaah (khawf) and so on, the likes of which were not found in the rest of the inhabitants of other lands.
Abush-Shaikh Al-Asbahaanee reported with a chain of narration connected to Muhammad bin Sireen that it reached him that a group of people preferred wearing wool, so he said: ‘There are some people that prefer to wear wool claiming that they resemble the Messiah, son of Maryam. However, the guidance of our Prophet (sallAllaahu ‘alayhi wa sallam) is more beloved to us, and he (sallAllaahu ‘alayhi wa sallam) would wear cotton and other types of clothes.’ Or he stated words similar to this.”
Then he (Ibn Taimiyyah) said after this: “These people ascribe themselves to outer garments, which in this case is wool (soof) garments. So it can be said about one of them that he is a Soofee. However, their methodology is not restricted to the wearing of woolen garments, nor do they mandate that on anyone or adhere to ordering it. They only attach themselves to it due to it being the outer condition.”
Then he said: “So this is the origin of Soofiyyah (Sufism). After this, it branched off and diversified.” 
Ibn Taimiyyahs words, may Allaah have mercy on him, indicate that Sufism originated in the lands of Islaam at the hands of some very pious worshippers from Basrah as a result of their going to great lengths in abstinence (zuhd) and worship (‘ibaadah). Then after that, Sufism evolved and changed.
The conclusion that some modern-day authors have come to – that Sufism crept into the lands of the Muslims from other religions, such as Hinduism and Christian monasticism – has become accepted based on what Shaikh Ibn Taimiyyah reported from Muhammad bin Sireen, that he said: “There are some people that prefer to wear wool claiming that they resemble the Messiah, son of Maryam. However, the guidance of our Prophet (sallAllaahu ‘alayhi wa sallam) is more beloved to us!” This indicates that Sufism has a connection to the religion of the Christians!!
Dr. Saabir At-Tu’aimah said in his book: “Sufism – Its Beliefs and Methods”: “It appears that it came about due to the influence of Christian monasticism in which the monks would wear woolen garments and reside in their monasteries. There were many of them that would be upon this practice throughout the lands, which Islaam freed by way of Tawheed…” 
Shaikh Ihsaan Ilaahee Dhaheer, may Allaah have mercy on him, said in his book “Sufism: Its Source and Origin”: “When we look deep into the teachings of the first and latter-day Sufis and the statements that have been quoted and narrated from them in the Sufi books of old and present, we see a huge difference between it and the teachings of the Qur’aan and the Sunnah. Likewise, we don’t see its roots or its seeds in the history of the chief of all creations (Prophet Muhammad) (sallAllaahu ‘alayhi wa sallam) nor in that of his righteous and noble Companions, from the best of Allaah’s creation. Rather, contrary to that, we see that it has been derived and acquired from Christian Monasticism, Brahmanism, Hinduism, the religious devotion of Judaism and the asceticism of Buddhism.” 
Shaikh ‘Abdur-Rahmaan Al-Wakeel, may Allaah have mercy on him, said in the introduction of the book “The Downfall of Sufism”: “Indeed, Sufism is the lowest and vilest of schemes, which the Devil innovated so that the servants of Allaah can mock and ridicule along with him in his war against Allaah and His Messengers. It is the veil of the Magians (Majoos), which gives the impression that it is divine. Rather, it is the veil of every enemy to the true religion. Examine it and you will find in it Brahmanism, Buddhism, Zoroastrianism, and the Manichaean beliefs. You will find Platonism in it. You can even find Judaism, Christianity and the idolatry of the Days of Ignorance in it.” 
Through presenting the views of these modern-day writers regarding the origin of Sufism, as well as many other writers not mentioned here that hold these same views, it becomes clear that Sufism is a foreign concept that was introduced into Islaam. This shows in the practices of those who ascribe themselves to it – those practices that are foreign to Islaam and far removed from its guidance. By this, we intend the latter-day adherents to Sufism whose mystical illusions and fantasies have become many and great.
But as for the former predecessors, such as Al-Fudayl bin ‘Iyyaad, Al-Junaid, Ibraaheem bin Adham and others, then they were upon a state of moderateness.
 Translator’s Note: The Ahlus-Suffah (People of the Bench) referred to the poorer Companions who would sit outside the Prophet’s (sallAllaahu ‘alayhi wa sallam) masjid, waiting for charity and waiting for the Prophet (sallAllaahu ‘alayhi wa sallam) to come out so that they could accompany him and learn hadeeth from him.
 Majmoo’-ul-Fataawaa (11/5-7, 16, 18)
 As-Sufiyyah: Mu’taqidan wa Maslakan (pg. 17)
 At-Tasawwuf: Al-Mansha’ wal-Masdar (pg. 28)
 Masra’ at-Tasawwuf (pg. 19)
Published: September 18, 2004 | Modified: September 18, 2004