Sahih Al Bukhari (668)

عن طلحة بن عبيد الله يقول {جاء رجل إلى رسول الله (صلى الله عليه وسلم) فإذا هو يسأله عن الإسلام فقال رسول الله (صلى الله عليه وسلم) خمس صلوات في اليوم والليلة فقال هل علي غيرها قال لا إلا أن تطوع فقال رسول الله (صلى الله عليه وسلم) وصيام شهر رمضان قال هل علي غيره قال لا إلا أن تطوع قال وذكر له رسول الله (صلى الله عليه وسلم) الزكاة قال هل علي غيرها قال لا إلا أن تطوع فأدبر الرجل وهو يقول والله لا أزيد على هذا ولا أنقص قال رسول الله (صلى الله عليه وسلم) أفلح إن صدق}

Talhah ibn `Ubaydullah narrated: A man came to Allah's Messenger (peace be upon him) asking him about Islam, Allah's Messenger (peace be upon him) said: "You have to offer five compulsory prayers in a day and a night (24 hours)." The man asked: "Is there any more compulsory prayers for me?" Allah's Messenger (peace be upon him) said: "No, unless you like to offer Nawafil (i.e. optional prayers)." Allah's Messenger (peace be upon him) then added: "You have to observe fasts during the month of Ramadan." The man said: "Am I to fast any other days?' Allah's Messenger (peace be upon him) said: "No, unless you wish to observe the optional fast voluntarily." Then Allah's Messenger (peace be upon him) told him about the compulsory Zakat. The man asked: "Do I have to give anything besides?" Allah's Messenger (peace be upon him) said: "No, unless you wish to give in charity voluntarily." So, the man departed saying: "By Allah I will neither do more nor less than that." Allah's Messenger (peace be upon him) said: "If he has said the truth he will be successful."