Volume 8 · Book 76 · Hadith 559t
Narrated Sahl bin Sa'd: Allah's Apostle said, "In Paradise there is a tree so big that in its shade a rider may travel for one hundred years without being able to cross it."
— Sahih Bukhari, Volume 8, Book 76: To make the Heart Tender (Ar-Riqaq), Hadith #559t