After his graduation, Thanwi taught religious sciences in Kanpur for fourteen years. Over a short period of time, he acquired a reputable position as a religious scholar of Sufism among other subjects. His teaching attracted numerous students, and his research and publications became well known in Islamic institutions. During these years, he traveled to various cities and villages, delivering lectures in the hope of reforming people. Printed versions of his lectures and discourses would usually become available shortly after these tours. Until then, few Islamic scholars had had their lectures printed and widely circulated in their own lifetimes. The desire to reform the masses intensified in him during his stay at Kanpur.
Eventually, Thanwi retired from teaching and devoted himself to reestablishing the spiritual centre (khānqāh) of his shaikh in Thāna Bhāwan.
In 1906 Ahmad Raza Khan issued a fatwa against Thanwi and other Deobandi leaders entitled Husam ul-Haramain (Urdu: Sword of Mecca and Medina), decrying them as unbelievers and Satanists. The fatwa was also signed by other scholars including from Hijaz.
The scholars of Deoband wrote The Sword on the Disproved (Al-Muhannad ‘ala al-Mufannad) in reply, seeking to refute Reza Khan's allegations.
^Ali Abbasi, Shahid. (2008, January–March). Rethinking in Islam: Mawlana Ashraf 'Ali Thanawi on Way and Way-faring. Hamdard Islamic-us, 21(1), 7–23. (Article on Ashraf 'Ali's teachings on Sufism.)
^Fatwa of Kufr (originally issued 1900 C.E.), posted at SufiManzil.org