Sahih Muslim Book 26, Hadith Number 5411.

Chapter : If a person goes away from the place occupied by him, he has a better right to occupy it after coming back.

Ibn ‘Umar reported Allah’s Messenger (may peace be upon him) as saying: None should make one’& brother stand and then sit at his place (and it was common with) Ibn Umar that when any person stood in the company (with a view to making room for him) he did not sit there.