Who was a famous Persian Sufi who lived in the 11th century in Herat who's works refer to a particularly important group of God's saints?
Abdal Abdāl ("lit": substitutes, but which can also mean "generous" ["karīm"] and "noble" ["sharīf"]) is a term used in Islamic metaphysics and Islamic mysticism, both Sunni and Shiite, to refer to a particularly important group of God's saints. In the tradition of Sunni Islam in particular, the concept attained an especially important position in the writings of the Sunni mystics and theologians, whence it appears in the works of Sunni authorities as diverse as Abu Talib al-Makki (d. 956), Ali Hujwiri (d. 1072), Ibn Asakir (d. 1076), Khwaja Abdullah Ansari (d. 1088), and Ibn Khaldun (d. 1406).
Salaf Salaf (Arabic: سلف‎ ‎ , "ancestors" or "predecessors"), also often referred to with the honorific expression of "al-salaf al-ṣāliḥ" (Arabic: السلف الصالح‎ ‎ , "the pious predecessors") are often taken to be the first three generations of Muslims, that is the generations of the Islamic Prophet Muhammad and his companions (the Sahabah), their successors (the Tabi‘un), and the successors of the successors (the Taba Tabi‘in).