Sahih Muslim Book 18, Hadith Number 4286.
Chapter : Entertainment of the Guest.
Abd Shuraib al-Adawi reported: My eare listened and my eye saw when Allah’s Messenger (may peace be upon him) spoke and said: He who believes In Allah and the hereafter should show respect to the guest even with utmost kindness and courtesy. They said: Messenger of Allah, what is this utmost kindness and courtesy? He replied: It is for a day and a night. Hospitality extends for three days, and what is beyond that is a Sadaqa for him; and he who believes in Allah and the Hereafter should say something good or keep quiet.