Sahih Bukhari Volume 7, Book 63, Hadith Number 221.

Narrated By Sahl bin Sad As-Sa’idi : (A companion of Allah’s Apostle) Allah’s Apostle, holding out his middle and index fingers, said, “My advent and the Hour’s are like this (or like these),” namely, the period between his era and the Hour is like the distance between those two fingers, i.e., very short.