Sahih al-Bukhari 50

Musaddad narrated to us. He said: Ismail ibn Ibrahim narrated to us. He said: Abu Hayyan al-Taymi narrated to us, from Abu Zur'a, from Abu Hurayra, who said: One day the Prophet (peace and blessings be upon him) appeared before the people. Gabriel came to him and asked: ‘What is faith?’ He replied: ‘Faith is to believe in Allah, His angels, the meeting with Him, His messengers, and the resurrection.’ He asked: ‘What is Islam?’ He replied: ‘Islam is to worship Allah and not associate anything with Him, to establish the prayer, give the obligatory zakat, and fast Ramadan.’ He asked: ‘What is ihsan?’ He replied: ‘It is to worship Allah as though you see Him; if you do not see Him, then He sees you.’ He asked: ‘When is the Hour?’ He replied: ‘The one who is asked about it knows no more than the one who asks. I will tell you about its signs: when the slave woman gives birth to her master, and when the barefoot herders of dark camels vie with one another in raising buildings. Among five things, none knows them except Allah.’ Then the Prophet (peace and blessings be upon him) recited: ‘Indeed, with Allah is the knowledge of the Hour...’ Then Gabriel turned away, and the Prophet said: ‘Bring him back.’ But they saw nothing. He said: ‘This was Gabriel; he came to teach the people their religion.’ Abu Abdullah said: He included all of that as part of faith.