Maktubat-i Imam Rabbani (Quddisa Sirrahu)

Maktubat-i Imam Rabbani :[MAKTUBAT E SHAREEF]
The ‘Letters of al-Imam Rabbani Mujaddid e Alf Thani’ (Islamic
Renovator of 2nd Milleneum of Hijra) Shaykh Ahmad Sirhindi
al Faruqi an Naqshbandi Hanafi al Maturidi (Qaddasallahu Sirrahul Aziz)                    (d.1034.AH.Sirhind Shareef ,Punjab,India).
Original Language: Persian (some in Arabic) ,  the official language of Mughal Emperors of India.
Volumes: Three. 
Maktubat is a common term referred to the letters of Sufi sheikhs and Islamic Scholars.
The Maktubat of Sheikh Ahmed Sirhindi are indeed the most popular among the letters of Sufi sheikhs. This book is a classical and most venerated book of Sufism that covers classical Sufism, the methodologies, beliefs and practices of Islam and many other spiritual secrets on the Higher Realities(Haqaiq) of Islam.
Letters of Sheikh Ahmed Sirhindi (may Allah be pleased with him) were compiled in his lifetime. Three volumes were compiled, as detailed below:
Volume 1 contains 313 letters, and was compiled by Khwajah Yar Muhammad Badakhshi Talqani (rahmatullah alaih), a murid of Sheikh Ahmed Sirhindi. The volume was named as Durr al-Ma'rifat (در المعرفت ) and was finished in 1025 AH, as the Sheikh ordered to complete it at 313 letters, 313 being a sacred number.
Volume 2 was named as Noor al-Khalaiq (نور الخلاق) and contains 99 letters. It was compiled by Khwajah Abdul Hayy.
Volume 3 was compiled by Khwajah Muhammad Hashim Kashmi and contains 124 letters. The volume was named Ma'rifat al-Haqa'iq (معرفت الحقائق ).
Translations:
Maktubat Sheikh Ahmed Sirhindi have been translated in many languages.
 Urdu translation  is by Maulana Saeed AhmedNaqshbandi (rh) . Another popular Urdu translation of the complete book is by Sayyad Zawwar Hussain Shah Naqshbandi, a famous Sheikh of Naqshbandisufi order.
Arabic translation was completed by Sheikh Muhammad Murad Makki, a Naqshbandi sheikh of 19th century.
 English:
More than 100 selected letters are translated by Huseyn Hilmi Isik an Naqshbandi of Istanbul, Turkey (d.1422.AH)  and spread through out his publications and are especially available in the first 3 Volumes of Endless Bliss. He translated them into Turkish and his disciples undertook the English translations. ( Simple English)
http://www.hizmetbooks.org/AdobeBooks/bliss-1.pdf
http://www.hizmetbooks.org/AdobeBooks/bliss-2.pdf
http://www.hizmetbooks.org/AdobeBooks/bliss-3.pdf
 Maktubat in Arabic,Persian and Other languages are available here:
http://www.hakikatkitabevi.com/
Some of the letters, especially referring to Higher Spiritual Knowledge (Haqiqah) have been recently translated into better English by Sufi Irshad Aalam and can be read here:
 
http://www.sufipeace.org/

Shaykh Husain Hilmi Effendi (rah)(d.1422 Hjri,Istanbul,Turkey):
He read books by the scholars of Islam and quoted with tearful eyes the sayings of al-Imam ar-Rabbani Mujaddid e Alf Thani’  Shaykh Ahmad Sirhindi (qs) &Syed  'Abdul Hakim Arwasi(QS) (d.1364.Hijri,Ankara,Turkey ).
 He said, "Kalam-i kibar, kibar-i kalamast." (The words of the superiors are the superior words.)
He frequently quotes 'Abdul Hakim Effendi is having said: "Not everybody can understand al-Imam ar-Rabbani's Maktubat, which resembles neither Hafiz-i Shirazi's poems nor the Khamsa. We read it not to understand it but to be blessed by reading it."
http://www.hizmetbooks.org/Proof_of_Prophethood/prhuseyn.htm