The Prophet ﷺ said, "Hospitality to a guest is for three days. Anything beyond that is charity."
عن النبي ﷺ قال: الضيافة ثلاثة أيام، فما سوى ذلك فهو صدقة.
Abu Dawud (3749) and Ahmad (8645) both narrated it from the hadith of Hammad bin Salama, from Asim, from Abu Salih, from Abu Hurairah, who mentioned it. Its chain of transmission is hasan because of Asim, who is Ibn Abu Najud, for his hadith is hasan. Ibn Hibban graded it sahih (5284), and narrated it through another route from Abu Hurairah.