Musannaf Ibn Abi Shayba 28:945

Ibn ‘Uyaynah narrated to us, from Ibn ‘Ajlan, from Sa‘id ibn Abi Sa‘id, from Abu Shurayh al-Khuza‘i, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever believes in Allah and the Last Day, let him honor his guest. His prize is a day and a night. It is not lawful for a guest to stay with his host until he causes him hardship. Hospitality is three days, and whatever is spent on him after three days is charity."