Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: The Prophet (peace and blessings be upon him) said: "Hospitality is for three days; whatever is beyond that is charity."
Imam al-Tabarani recorded it in al-Mu'jam al-Awsat. Its chain contains a narrator, Rishdin bin Kurayb, and he is da'if (weak).