The prolific scholar and polymath al-Bīrūnī dictated his Book of Pharmacy (Kitab al-Saydanah) about 1045 in present-day Afghanistan. A copy of that manuscript made in 1076 begins with an encomium:
The Kitab al-Saydanah has been indited by a great philosopher, a scholar of immense magnitude, a master of erudition, a master of wisdom, an example for his followers and the contemporaries, an axis round which profound axioms and observations revolve, the circumscriber of the apparent and the hidden, a past master of knowledge derived from observations, a possessor of high station among men, a mathematician besides whose work that of his predecessors — either before or after Islam — pales into insignificance, a personality that is both unique and singular, and worthy of reverence and exaltation, Sayyedonā-wa-Mawlānā, a great teacher, Abū al-Rayḥān Muḥammad ibn Aḥmad al-Bīrūnī, may God vouchsafe on him eternal repose, and shower blessings on his grave! May God be pleased with him and accord him a place among the exalted and blest! 
This manuscript was copied in 1154. Some additional text was then appended:
From the commencement of this book down to the nineteenth part, the authorship seems to have been that of a man who displays madness, lack of sapience, (an array of) unauthorized opinions, an unbalanced mind, insanity, foul temperament, disturbance, and superstition, and whose pseudonym is Dew Dast. I have done my best to introduce whatever corrections and emendations I could, but, despite the best of efforts, could not achieve it to my satisfaction, since the copying was extremely bad and it was riddled with mistakes. I have lavished a great deal of time on this work. Whatever errors I could detect, I have corrected and, wherever I came across an egregious shortcoming or defect, I made it good.
I have stated this so that the readers may know whose fault it is, so that they may not attribute it to the author or someone else. God alone knows best. 
Current scholarly evaluations decisively rate al-Bīrūnī as brilliant, rather than insane. The contrasting perspectives, however, are more interesting than one being correct, and the other, wrong.
The opening encomium is in the style of scholarly praise in the early Islamic world. Such praise isn’t just the piling up of extravagant epithets. Describing al-Bīrūnī as a “great philosopher” links him to Greek knowledge. Al-Bīrūnī quotes extensively in his work the Greek authorities Dioscorides, Galen, Oribasius, and Paulus Aegineta. Master of erudition and wisdom suggests detailed study of the texts produced through centuries of Islamic scholarship. Al-Bīrūnī frequently references Islamic scholars who have preceded him. The epithet “past master of knowledge derived from observations” seems to acknowledge, with its adjective “past,” that al-Bīrūnī was then old, blind, and nearly deaf. Al-Bīrūnī’s text contains detailed observations of the natural world. These observations al-Bīrūnī evidently made when he was younger and in better health. Describing al-Bīrūnī as a mathematician emphasizes that al-Bīrūnī also had aptitude for abstract thought. Al-Bīrūnī’s writings cover mathematics, astrology, pharmacology, geology, history, and the people and culture of India. His scholarly work is of remarkable range.
Al-Bīrūnī scholarly range is evident even within his Book of Pharmacy. Discussing the term for apothecaries, al-Bīrūnī quotes hadith and Arabic poetry, and then moves on to the origin of the Arabic word saydanani:
Some etymologists have held that saydanani is a longish worm having so many legs that it is almost impossible to count them, since they are of various sizes, big and small. On this basis they have held that the work saydanani comes from this worm, as in this art several kinds of drugs, big and small, are the tools of the apothecary. This exercise in etymology is absolute foolish and baseless talk. Probably what is implied is the insect that enters the human ear and which is called by some al-arba’wa al arba-in (forty-four) and by some others as-saba-wa-al-sab’in (seventy-seven). I once had the occasion to count the legs of this insect; they came to two hundred and forty.
A scholar who would count 240 legs on a insect is a serious scholar indeed.
The appended disparaging text seems to be concerned with orthodoxy. Accusing al-Bīrūnī of presenting “unauthorized opinions” and “superstition” presumes that al-Bīrūnī’s should present only authorized opinions and scientific facts, as recognized at that time. Al-Bīrūnī’s text, in contrast, brings together a wide variety of material with historical and encyclopedic dimensions. That intellectual scope seems to have subsequently fallen out of favor.
* * * * *
- al-Bīrūnī’ on substitute medicines
- the ancient pharmaceutical profession
- status economy in the early Islamic world
 Trans. Said (1973) p. 1.
 Id. p. 344. This apparently was writing of Shaikh Imam Muhammad bin Zaki al-Ghaznavi. Other text from the introduction describes technical difficulties with the manuscript: illegible words, orthographical errors, apocopations, transpositions, and transformations of words.
 Id. p. 9. Al-Bīrūnī also describes himself as being eighty years old.
Said, Hakim Mohammed. 1973. Abu-‘r-Raiḥān Muḥammad Ibn-Aḥmad al-Bīrūnī. Al-Biruni’s book on pharmacy and materia medica 1. /ed. with English transl. by Hakim Mohammed Said. Karachi: Hamdard National Foundation.