Sahih Muslim Book 040, Hadith Number 6786.

Chapter : There is in paradise a tree under the shadow of which a rider can travel for a hundred years and even then he would not be able to cover it.

Sahl b. Sa'd reported Allah's Messenger (may peace be upon him) as saying: In Paradise, there is a tree under the shadow of which a rider can travel for a hundred years without covering (the distance) completely. This hadith has also been transmitted on the authority of Abu Sa'id al-Khudri that Allah's Apostle (may peace be upon him) is reported to have said: In Paradise, there is a tree under the shadow of which a rider of a fine and swift-footed horse would travel for a hundred years without covering the distance completely. There would be the pleasure of Allah for the inmates of Paradise and He would never be annoyed with them.