Sahih Bukhari Volume 002, Book 026, Hadith Number 594.

Narated By Abu Huraira : The Prophet was asked, "Which is the best deed?" He said, "To believe in Allah and His Apostle." He was then asked, "Which is the next (in goodness)?" He said, "To participate in Jihad in Allah's Cause." He was then asked, "Which is the next?" He said, "To perform Hajj-Mabrur."