An Introduction to Irfan
Gradually this became the standard practice, and mystical concepts were expressed in the form of love-poetry (ghazal) and symbolic expressions. Some believe that Dhu al-Nun also introduced many Neoplatonic ideas into 'irfan and sufism. Dhu al-Nun died in 246/860 in Cairo.
7. Sahl ibn 'Abd Allah al-Tustari:
He is one of the great 'urafa' and sufis. A sect of gnostics who consider the main principle of spirituality to be combatting the self is named 'Sahliyyah' after him. He associated with Dhu al-Nun of Egypt at Mecca. He died in Basrah in 282/895. 
8. Husayn ibn Mansur al-Hallaj:
Now famous simply as al-Hallaj, he is one of the most controversial mystics of the Islamic world. The shathiyyat uttered by him are many, and he was accused of apostasy and claiming divinity. The jurisprudents pronounced him an apostate and he was crucified during the reign of the 'Abbasid caliph al-Muqtadir. The 'urafa' themselves accuse him of disclosing spiritual secrets. Hafiz has this to say about him:
He said, that friend, who was raised high on the cross,
Some consider him no more than a juggler, but the 'urafa' themselves absolve him and say that the statements of al-Hallaj and Bayazid that gave the impression of unbelief were made when they were beside themselves in the state of 'intoxication'.
Al-Hallaj is remembered by the 'urafa' as a martyr. He was executed in 309/913. 
'Urafa' of the Fourth/Tenth Century:
1. Abu Bakr al-Shibli:
A pupil and disciple of Junayd of Baghdad and one who had met al-Hallaj, al-Shibli is one of the famous mystics. He was originally from Khurasan. In the book Rawdat al-jannat, and in other biographies, many mystical poems and sayings have been recorded of him.
Khawajah 'Abd Allah al-'Ansari has said: "The first person to speak in symbols was Dhu al-Nun of Egypt. Then came Junayd and he systematized this science, extended it, and wrote books on it. Al-Shibli, in his turn, took it to the pulpit." Al-Shibli; died in 334/846 at the age of 87.
2. Abu 'Ali al-Rudbari:
He traced his descent to Nushirwan and the Sasanids, and was a disciple of Junayd. He studied jurisprudence under Abu al-'Abbas ibn Shurayh, and literature under Tha'lab. Due to his versatile knowledge, he was called the 'collector of the Law, the Way, and the Reality' (jami' al-Shari'ah wa al-Tariqah wa al-Haqiqah). He died in 322/934.
3. Abu Nasr al-Sarraj al-Tusi:
Abu Nasr al-Sarraj is the author of the book al-Luma', one of the principal, ancient and reliable texts of 'irfan and sufism. Many of the shaykhs of the sufi orders were his direct or indirect pupils. He passed away in 378/988 in Tus.