Musnad Abu Ya'la al-Mawsili 160:195

Wahb ibn Baqiyyah narrated to us, Khalid informed us, from Abd al-Rahman ibn Ishaq al-Madani, from Sa'id ibn Abi Sa'id, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever believes in Allah and the Last Day, let him honor his guest. His prize is three [days], and whatever is beyond that is charity. And it is not lawful for him to stay with him until he causes him to be sinful."