According to rahyafte (the missionaries and converts website)
About Abū Hamzā Thumālī (r)
His name was Thābit b. Safiya and was known as Abū Hamza Thumālī. He was a contemporary of Imam Ali Zaynul „Ābidīn (a). Commenting on the worship of his master he said, “I have never heard that there is a person more ascetic than Ali b. al-Husayn, who caused to weep all those were in his presence when he talked about asceticism and preaching.” He has related that during the month of Ramadhān Imam as-Sajjād (a) spent a greater part of the night in prayers and when it was the time of beginning of the fast he recited the following dua’a. This Du„ā‟ has been recorded in the book Misbāh and also appears in Abbas Qummī‟s Mafātīhul Jinān.
Ayatullah Khumayni (q) on the Du‘ā:
Read the invocation of Abū Hamza Thumālī as uttered by Imam Sayyid as-Sājidīn Zaynul `Ābidīn (a). Reflect upon its subject matter and think for a while on their words. Nowhere are we required to make a rapid reading of this lengthy supplication without pondering over its meaning. You and I are not blessed with the spiritual state of al-Imam as-Sajjād (a) to be able to recite the whole Du„ā‟ in a sustained ecstasy at one time. Try to read one third or one fourth of it every night with feeling and meditate upon its words.
The Arabic text along with English translation of this famous supplication (PDF)
Source: http://www.tayyiba.org
