With these poets Arabic literature reached its highest development. They are the true expression of the free Arabic spirit. Most of them lived before or during the time of the appearance of Muhammad. His coming produced a great change in the life of the simple Bedouins. Though they could not be called heathen, their religion expressed itself in the simple feeling of dependence upon higher powers, without attempting to bring this faith into a close connection with their daily life. Muhammad introduced a system into which he tried to mold all things. He wished to unite the scattered tribes to one only purpose. He was thus cutting away that untrammeled spirit and that free life which had been the making of Arabic poetry. He knew this well. He knew also the power the poets had over the people. His own 'Qur'an' (Koran) was but a poor substitute for the elegant verses of his opponents. "Imr-al-Kais," he said, "is the finest of all poets, and their leader into everlasting fire." On another occasion he is reported to have called out, "Verily, a belly full of matter is better than a belly full of poetry." Even when citing verses, he quoted them in such a manner as to destroy the metre. Abu Bekr very properly remarked, "Truly God said in the 'Qur'an,' 'We have not taught him poetry, and it suits him not.'" In thus decrying the poets of "barbarism," and in setting up the 'Qur'an' as the greatest production of Arabic genius, Muhammad was turning the national poetry to its decline. Happily his immediate successors were unable or unwilling to follow him strictly. Ali himself, his son-in-law, is said to have been a poet; nor did the Umáyyid Caliphs of Damascus, "very heathens in their carnal part," bring the new spirit to its full bloom, as did the Abbassides of Bagdad.