For philosophic themes, consult:
T. J. DE BOER, "History of Philosophy in Islam" (London, 1903).
D. B. MACDONALD, "Development of Muslim Theology, Jurisprudence, etc."
(Scribners, New York, 1903).
J. L. BURCKHARDT, "Arabic Proverbs" (London, 1830).
And most important of all for general information is the new and
authoritative
"Encyclopædia of Islam," edited by Houtsma, Arnold, and Schaade.