http://hadith.al-islam.com/Display/Display.asp?Doc=0&Rec=2972

Collected by Imaam Bukhaari in his Saheeh vol. 3, Book 31, Hadeeth #115

From Qutaybah ibn Saeed from Isma’eel ibn J’affar from his father Abu Suhail from his father Talha ibn ‘Ubaidullaah:

A bedouin with unkempt hair came to Rasoolullaah sAllaahu alayhi wa salam and said, “O Rasoolullaah! Inform me what Allaah has made obligatory for me as regards the prayers.”

He (sAllaahu alayhi wa salam) replied: “You have to offer perfectly the five obligatory prayers in a day and night, unless you want to pray Nawafil.”

The bedouin further asked, “Inform me what Allaah has made obligatory for me as regards fasting.”

He (sAllaahu alayhi wa salam) replied, “You have to fast during the whole month of Ramadan, unless you want to fast more as Nawafil.”

The bedouin further asked, “Tell me how much Zakat Allaah has enjoined on me.”

Thus, Rasoolullaah (sAllaahu alayhi wa salam) informed him about all the rules (fundamentals) of Islaam. The bedouin then said, “By Him Who has honored you, I will neither perform any Nawafil nor will I decrease what Allaah has enjoined on me.”

Rasoolullaah (sAllaahu alayhi wa salam) said, “If he is saying the truth, he will succeed (or he will be granted Paradise).”

Also the hadeeth qudsi Imaam Bukhaari collected in His Saheeh, that Abu Hurairah (ra) reported Rasoolullaah (sAllaahu alayhi wa salam) said:

“Allaah the Almighty has said: ‘Whosoever acts with enmity towards a closer servant of Mine, I will indeed declare war against him. Nothing endears My servant to Me than doing of what I have made obligatory upon him to do. And My servant continues to draw nearer to Me with supererogatory (nawafil) prayers so that I shall love him. When I love him, I shall be his hearing with which he shall hear, his sight with which he shall see, his hands with which he shall hold, and his feet with which he shall walk. And if he asks (something) of Me, I shall surely give it to him, and if he takes refuge in Me, I shall certainly grant him it.’”