Musnad Ahmad 32:517

Hashim ibn al-Qasim narrated to us, Sulayman ibn al-Mughirah narrated to us, from Thabit, from Anas ibn Malik, who said: We had been forbidden from asking the Messenger of Allah, may Allah bless him and grant him peace, about anything. Thus, it used to please us when a wise man from the people of the desert would come and ask him while we were listening. A man from the people of the desert came and said: "O Muhammad, your messenger came to us and claimed to us that you claim that Allah sent you." He said: "He spoke the truth." He said: "Then who created the heaven?" He said: "Allah." He said: "Then who created the earth?" He said: "Allah." He said: "Then who set up these mountains and placed in them what He placed?" He said: "Allah." He said: "Then by the One who created the heaven and created the earth and set up these mountains, did Allah send you?" He said: "Yes." He said: "And your messenger claimed that we have five prayers in our day and our night." He said: "He spoke the truth." He said: "Then by the One who sent you, did Allah command you with this?" He said: "Yes." He said: "And your messenger claimed that we have zakat upon our wealth." He said: "He spoke the truth." He said: "Then by the One who sent you, did Allah command you with this?" He said: "Yes." He said: "And your messenger claimed that we have the fasting of a month in our year." He said: "He spoke the truth." He said: "Then by the One who sent you, did Allah command you with this?" He said: "Yes." He said: "And your messenger claimed that we have the pilgrimage to the House for whoever is able to find a way to it." He said: "He spoke the truth." He said: Then he turned away and said: "By the One who sent you with the truth, I will not add anything to them, nor will I decrease anything from them." The Prophet, may Allah bless him and grant him peace, said: "If he is truthful, he shall surely enter Paradise."