(1) باب وُجُوبِ الصِّيَامِ
It was narrated that Anas said:
"We were forbidden in the Quran to ask the Prophet about anything not imperative, so we liked it when a wise man from among the people of the desert came and asked him. A man from among the desert people came and said: 'O Muhammad, your messenger came to us and told us that you say that Allah, the Mighty and Sublime, has sent you.' He said: 'He spoke the truth.' He said: 'Who created the heavens?' He said: 'Allah.' He said: 'Who created the Earth?' He said: 'Allah.' He said: 'Who set up the mountains in it?' He said: 'Allah.' He said: 'Who created beneficial things in them?' He said: 'Allah.' He said: 'By the One Who created the heavens and the Earth, and set up the mountains therein, and created beneficial things in them, has Allah sent you?' He said: 'Yes.' He said: 'Your messenger said that we have to offer five prayers each day and night.' He said: 'He spoke the truth.' He said: 'By the One Who sent you, has Allah commanded you to do this?' He said: 'Yes.' He said: 'Your messenger said that we have to pay Zakah on our wealth.' He said: 'He spoke the truth.' He said: 'By the One Who sent you, has Allah commanded you to do this?' He said: 'Yes.' He said: 'Your messenger said that we have to fast the month of Ramadan each year.' He said: 'He spoke the truth.' He said: 'By the One Who sent You, has Allah commanded you to do this?' He said: 'Yes.' He said: 'Your messenger said that we have to perform Hajj, those who can afford it.' He said: 'He spoke the truth.' He said: 'By the One Who sent you, has Allah commanded you to do this?' He said: 'Yes.' He said: 'By the One Who sent you with the truth, I will not do more than this or less.' When he left, the Prophet said: 'If he is sincere, he will certainly enter paradise.'"
Reference: Sunan an-Nasa'i 2091
In-book reference: Book 22, Hadith 2
English translation: Vol. 3, Book 22, Hadith 2093