Lets examine what the Imams have to tell about Sufis
Imam Abu Hanifa (85 H. - 150 H)
"If it were not for two years, I would have perished." He said, "for two years I accompanied Sayyidina Ja'far as-Sadiq and I acquired the spiritual knowledge that made me a gnostic in the Way."
[Ad-Durr al-Mukhtar, vol 1. p. 43]
Imam Malik (95 H. - 179 H.)
"whoever studies Jurisprudence [tafaqaha] and didn't study Sufism [tasawwaf] will be corrupted; and whoever studied Sufism and didn't study Jurisprudence will become a heretic; and whoever combined both will reach the Truth."
['Ali al-Adawi , vol. 2, p 195.]
Imam Shafi'i (150 - 205 AH.)
"I accompanied the Sufi people and I received from them three knowledges: ...how to speak; how to treat people with leniency and a soft heart... and they... guided me in the ways of Sufism."
[Kashf al-Khafa, 'Ajluni, vol. 1, p 341.]
Imam Ahmad bin Hanbal (164 - 241 AH.)
"O my son, you have to sit with the People of Sufism, because they are like a fountain of knowledge and they keep the Remembrance of Allah in their hearts. they are the ascetics and they have the most spiritual power."
[Tanwir al-Qulub p. 405]
Ibn Taymiyya (661 - 728 AH)
"Tasawwuf has realities and states of experience which they talk about in their science. Some of it is that the Sufi is that one who purifies himself from anything which distracts him from the remembrance of Allah and who will be so filled up with knowledge of the heart and knowledge of the mind to the point that the value of gold and stones will be the same to him. And Tasawwuf is safeguarding the precious meanings and leaving behind the call to fame and vanity in order to reach the state of Truthfulness, because the best of humans after the prophets are the Siddiqeen, as Allah mentioned them in the verse:
"(And all who obey Allah and the Apostle) are in the company of those on whom is the grace of Allah: of the prophets, the sincere lovers of truth, the martyrs and the righteous; Ah! what a beautiful fellowship." (an-Nisa', 69,70)
"...some people criticised Sufiyya and Tasawwuf and they said they were innovators, out of the Sunnah, but the truth is they are striving in Allah's obedience [mujtahidin fi ta'at-illahi], as others of Allah's People strove in Allah's obedience. So from them you will find the Foremost in Nearness by virtue of his striving [as-saabiq ul-muqarrab bi hasab ijtihadihi]. And some of them are from the People of the Right hand [Ahl al-Yameen mentioned in Qur'an in Sura Waqi'ah], but slower in their progress.... And this is the origin of Tasawwuf. And after that origin, it has been spread and [tasha'abat wa tanawa'at] has its main line and its branches.
[Majmu'a Fatawa Ibn Taymiyya al-Kubra, Vol. 11, Book of Tasawwuf, p. 497].
"The miracles of saints are absolutely true and correct, by the acceptance of all Muslim scholars. And the Qur'an has pointed to it in different places, and the Hadith of the Prophet (s) has mentioned it, and whoever denies the miraculous power of saints are only people who are innovators and their followers." [al-Mukhtasar al-Fatawa, page 603]. Ibn Taymiyya says, "what is considered as a miracle for a saint is that sometimes the saint might hear something that others do not hear and they might see something that others do not see, while not in a sleeping state, but in a wakened state of vision. And he can know something that others cannot know, through revelation or inspiration."
[Majmu'a Fatawi Ibn Taymiyya, Vol. 11, p. 314].
