[Sidenote: THE QADI ABU YUSUF] This method, as we shall see later, was vehemently attacked by his opponents, as was his system in general. Yet that system by its philosophical perfection—due to its theoretical origin—and perfection in detail—due to generations of practical workers—has survived all attack and can now be said to be the leading one of the four existing schools. No legal writings of Abu Hanifa have reached us, nor does he seem to have, himself, cast his system into a finished code. That was done by his immediate pupils, and especially by two, the Qadi Abu Yusuf, who died in 182, and Muhammad ibn al-Hasan, who died in 189. The first was consulting lawyer and chief Qadi to the great Khalifa Harun ar-Rashid, and, if stories can be believed, proved himself as complaisant of conscience as a court casuist need be. Innumerable are the tales afloat of his minute knowledge of legal subtleties and his fertility of device in applying them to meet the whims of his master, Harun. Some of them have found a resting place in that great mirror of mediæval Muslim life, _The Thousand and One Nights_; reference may be made to _Night 296_. Through his influence, the school of Abu Hanifa gained an official importance which it never thereafter lost. He wrote for Harun a book which we have still, on the canon law as applied to the revenues of the state, a thorny and almost impossible subject, for the canon law makes really no provision for the necessary funds of even a simple form of government and much less for such an array of palaces and officials as had grown up around the Abbasids. His book is marked by great piety in expression and by ability of the highest kind in reconciling the irreconcilable.