Sahih Bukhari Volume 002, Book 023, Hadith Number 479.
Narated By Abu Aiyub : A man said to the Prophet "Tell me of such a deed as will make me enter Paradise." The people said, "What is the matter with him? What is the matter with him?" The Prophet said, "He has something to ask. (What he needs greatly) The Prophet said: (In order to enter Paradise) you should worship Allah and do not ascribe any partners to Him, offer prayer perfectly, pay the Zakat and keep good relations with your Kith and kin." (See Hadith No. 12, Vol 8).