Sahih al-Bukhari 26

Narrated Abu Huraira: Allah's Messenger (ﷺ) was asked, "What is the best deed?" He replied, "To believe in Allah and His Messenger (Muhammad). The questioner then asked, "What is the next (in goodness)? He replied, "To participate in Jihad (religious fighting) in Allah's Cause." The questioner again asked, "What is the next (in goodness)?" He replied, "To perform Hajj (Pilgrim age to Mecca) 'Mubrur, (which is accepted by Allah and is performed with the intention of seeking Allah's pleasure only and not to show off and without committing a sin and in accordance with the traditions of the Prophet)."