The custom of writing poetry in honor of the Prophet began during his lifetime, when his associates, Kab ibn Zuhayr and Hassan ibn Thabit, praised him in rhyme. In the decades afterwards, countless poets have written nats, or poems in honor of Muhammad, in nearly every language of the Islamic world. Many of these poems are quite short, but some span hundreds of lines. Muhammad is said to have enjoyed this poetic tribute and he himself encouraged more poetry to be written about him. He was particularly fond of one poem by Ka'b ibn al-Ashraf that included a description of a night journey he (Ka'b) made to meet Muhammad. The latter asked him to stay with him and eat from his table, which pleased Ka'b greatly since he was very hungry. Then Muhammad told him to sleep with him under his blanket, which again pleased Ka'b since he was very tired. Finally, he said to tell others that Allah's peace be upon him and give charity as long as you live, which made Ka'b happy since he was very poor. This is one of the few poems about Muhammad that has survived into modern times. It is reported that when Uthman, who was then serving as the fourth caliph, ordered all poetry about Muhammad to be destroyed, many poems had already been written.