A good starting place for Judeo-Sufi studies...

Rabbeinu Bachya ibn Paqudah's Duties of the Hearts. Known in Arabic as Al-Hidayah ila Fara'id al-Qulub. In the Hebrew translation from the Judeo-Arabic, it is known as Chovot ha'Levavot, a text studied in Orthodox Yeshivot still today.

http://www.amazon.com/Direction-Duties-Littman-Library-Civilization/dp/1904113230

The next book, Al-Bustan al-`Uqul (The Garden of Intellectual-Reasonings) is Rabbi Natanyel ibn al-Fayyumi. Like rabbeinu Bachya, he was a Neo-Platonist, influenced by the Ikhwan as-Safa and was also the head of the Jews of Yemen the generation before the Rambam. The Epistle to Yemen was to this man's son, one of several significant reasons arguing for its lack of total historicity...

http://www.amazon.com/Bustan-al-Ukul-Nathanael-ben-Fayyumi/dp/0543712834/ref=sr_1_fkmr0_1?ie=UTF8&qid=1284477209&sr=1-1-fkmr0

The son of the Rambam, Avraham ben Maimonides, authored the Kitaab Kifayat al-`Abideen, (Comprehensive Guide to the Servants), a book which famously praised the Sufis of Islaam and called for the readoption of their ancient Jewish practices by the Egyptian Jewish community which he led. This is actually a very bad translation and not even the whole book. This was translated from the HEBREW translation from the Judeo-Arabic, and as i said, it is not even the whole thing. But the Judeo-Arabic translation is very long out of print. i have a copy that my son is scanning in, but it's not ready yet (still a lot to scan).

http://www.amazon.com/Guide-Serving-Torah-Classics-Library/dp/1583309810/ref=sr_1_1?s=books&ie=UTF8&qid=1284477257&sr=1-1

`Ovadyah ben Avraham ben Maimonides wrote an excellent Judeo-Sufi Treatise on the Pool, in Judeo-Arabic: Al-Mawalah al-Hawdiyyah

http://www.amazon.com/Treatise-Pool-Al-Mawala-Al-Hawdiyya/dp/0900860871/ref=sr_1_1?ie=UTF8&s=books&qid=1284477473&sr=1-1-spell

Natan'el Ibn Al-Fayyumi, Leader of the Jews of Yemen (ca. 1090-1165)

"Nothing prevents God from sending into His world whomsoever He wishes, since the world of holiness sends forth emanations unceasingly... Even before the revelation of the Law he sent prophets to the nations... and again after its revelation nothing prevented Him from sending to them whom He wishes so that the world might not remain without religion... Muhammad was a prophet to them but not to those who preceded them in the knowledge of God. He permitted to every people something He forbade to others. He sends a prophet to every people (Qur'aan 14.4) according to their language."

Ibn al-Fayyumi, the Bustan al-Ukul (ed. and trans. D. Levine; New York: Columbia University Press, 1908; repr. 1966), pp. 2 and el-Uqul: Gan ha'Sekhalim (Jerusalem: Halikhot Am Israel, AM 5744/1984)

Rabbeinu Aḅraham ben Rambam on the Jewish Origins of Sufi Practice

You are aware of the ways of the ancient saints of Israel, which are not of but little practise among our contemporaries, that have now become the practice of the Ṣūfīs of Islām, on account of the iniquities of Israel...

Aḅraham ben Maimonides, Kifāyat al-`Abidīn, Volume II, translated by Samuel Rosenblatt, (Baltimore, 1938), 266

Do not regard as unseemly our comparison of that to the behaviour of the Ṣūfīs, for the latter imitate the prophets and walk in their footsteps, not the prophets in theirs...

Ibid, 320

Observer then these wondrous traditions and sigh with regret over how they have been transferred from us and appeared amongst a nation other than ours whereas they have disappeared in our midst. My soul shall weep... because of the pride of Israel that was taken from them and bestowed upon the nations of the world...

Ibid, 322

The Qur'ān DOES NOT ABROGATE the Torah

"Oh People of the Book! You have no guidance [in life] until you maintain the observance of the Torah and the Gospel and that which has been revealed to you from your Lord; and certainly that which has been revealed to you [O Muhammad] from your Lord will make many of them [who do not observe the Torah or the Gospel's commandment to continue observing the Torah until Heaven and Earth pass away] to increase in rebellion and disbelief [in their aforementioned Scriptures]." - Qur'ān 5.68

قُلْ يَا أَهْلَ الْكِتَابِ لَسْتُمْ عَلَىٰ شَيْءٍ حَتَّىٰ تُقِيمُوا التَّوْرَاةَ وَالْإِنْجِيلَ وَمَا أُنْزِلَ إِلَيْكُمْ مِنْ رَبِّكُمْ ۗ وَلَيَزِيدَنَّ كَثِيرًا مِنْهُمْ مَا أُنْزِلَ إِلَيْكَ مِنْ رَبِّكَ طُغْيَانًا وَكُفْرًا ۖ فَلَا تَأْسَ عَلَى الْقَوْمِ الْكَافِرِينَ

Poetry from Baḥya

And if you do not grant me grace and forgive my transgression,
to whom shall I lift my eye?
If a master does not have compassion upon his servant and
forgive his guilt
To whom can he cry other than his master?...
Whither shall I go away from your spirit, and whither shall I flee?
If I go up to heaven, there you are; if I go down to Sheol, there
you are.
Therefore, from you to you I shall turn (mimkha elekha asurah)
From before you to you I shall flee (minegdekha `alekha evraḥah)
From your judgment to your mercy I run
From your quality of judgment to your quality of mercy I shall take refuge.

- Baḥya ibn Paqudah

Rabbi `Oḅadyah Maimūnī on the Inner-Shayṭān

Know, o brother, how vigilant a man would be, if he were to know that he has an enemy who, not content with destroying and suppressing him, is resolved to seize his wife, raper her in his presence and kill his children. He would be ever-vigilant, even while eating and drinking, sleeping or waking, to ward off his enemy.

As for the course to be followed, you must install the intellect in the center "upon the throne of his kingdom (Duet. 17.18). Then appoint the soul as his minister, the principal organs as close commanders and the secondary organs as servants in waiting, having each member carry out that which you deem appropriate. In this way, you will condemn your enemy and bind him "in fetters" and you will 'give judgment against him". (Jer 39.7, 5)

Therefore be sure to learn all the artifices with which he defense himself. "Neither shall your eye pity him", (Duet.12.9) for to be merciful towards evildoers is (to show them) inclemency, as the Sage has said, "For the mercy of the evil is cruel", (Prov. 12.10),

Chapter 13

At prayer time, purify your niyyah (intention) and be thoroughly mindful of what you say. Beware not to harbor thoughts of anything else but the object of your devotion, lest the serpent's venom penetrate you at the moment of inattention and render your du`a (supplication) unacceptable and to no avail.

Consequently, as a preliminary to prayer, it is fitting to prepare oneself through the wuḍū (ablution) of one's hands and fee, restoring and arousing thereby the soul. Furthermore, always recite a preliminary Psalm so that you kavvanah (singular concentration) be engaged and avoid praying in ruined places lest you entertain foreign thoughts. ... pay no attention to people who content themselves at prayer time with concentrating on the first verse of the Shema' and the first paragraph [of the `Amīdah], for the Truth shall show the Path.

Chapter 14

The Rambam on his son, Rabbeinu Aḅraham

Aḅraham ben Maimonides was a Judeo-Ṣūfī, author of Kifāyat al-`Abidīn, the head of the Egyptian Jewish community, who readopted the ancient Jewish practice of Salāh and instituted it for Egyptian Jewry. The Rambam said the following of his son, lest any imagine the controversial views and practices of Aḅraham were disavowed by his father:

When I consider the current state of the world, only two things console me: my involvement with wisdom, and the fact that my son Aḅraham has been blessed by God with the grace and the fits of the one whose name he bears [Aḅraham Aḅeinu] trusted, sustain, preserve, and lengthen my son's life and years. He is humble and unassuming when among others, in addition to all his other fine qualities. His mind grasps even the subtlest concepts, and he has a fine disposition. Without a doubt, he will be prominent among the great men of the generation, with God's help. I entreat God to watch over him and maintain His kindnesses to him. - Igros Ha'Rambam [Sheilat], vol. 1. p 424