Narrated Anas bin Malik:
While we were sitting with the Prophet(aees) in the mosque, a man came riding on a camel. He made his camel kneel down in the mosque, tied its foreleg and then said:
“Who amongst you is Muhammad?” At that time the Prophet(2 s) was sitting amongst us(his companions) leaning on his arm. We replied, “This white man reclining on his arm. The man then addressed him, “O Son of Abdul Muttalib.” answer your questions.” The man said to the Prophet, “I want to ask you something and will be hard in questioning. So do not get angry.” The Prophet said, “Ask whatever you want.” The man said, “I ask you by your Lord, and the Lord of those who were before you, has Allah sent you as an Apostle to all the mankind?” The Prophet Sn) replied, “By Allah, yes.” The man further said, “I ask you by Allah. Has Allah ordered you to offer five prayers in a day and night(24 hours).? He replied, “By Allah, Yes.” The man further said, “I ask you by Allah! Has Allah ordered you to observe fasts during this month of the year(i.e Ramadan)?” replied, “By Allah, Yes.” The man further said, “I ask you by Allah. Has Allah ordered you to take Zakat(obligatory charity) from our rich people and distribute it amongst our poor people?” The Prophet 5) replied, “By Allah, yes.” Thereupon that man said, “I have believed in all that with which you have been sent, and I have been sent by my people as a messenger, and i am Diman bin Thal Aba from the brothers of Bin Sad bin Bakar.
Reference (Sahih al-Bukhari )