Jami At Tirmidhi
1968
Sahih+3

Abu Shuraih Al-Kabi narrated that the Messenger of Allah said:: "Hospitality is for three days, and his reward is a day and a night, and whatever is spent on him after that is charity. And it is not lawful for him (the guest) to stay so long as to cause him harm

SahihAhmad Muhammad Shakir
SahihAl-Albani