Narrated Talha bin 'Ubaidullah: A man came to Allah's Apostle asking him about Islam, Allah's Apostle 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 Apostle said, "No, unless you like to offer Nawafil (i.e. optional prayers)." Allah's Apostle then added, "You have to observe fasts during the month of Ramadan." The man said, "Am I to fast any other days?' Allah's Apostle said, "No, unless you wish to observe the optional fast voluntarily." Then Allah's Apostle told him about the compulsory Zakat. The man asked, "Do I have to give anything besides?" Allah's Apostle 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 Apostle said, "If he has said the truth he will be successful."

Narrated `Abdullah: The Prophet said, "Whoever has to take an oath should swear by Allah or remain silent." (i.e. He should not swear by other than Allah.)