Sahih Muslim 2036 a
The Book of Drinks
What the guest should do if he is accompanied by someone who was not invited by the host; it is recommended for the host to give permission to the one who has accompanied the guest
Abu Mas'ud Ansari reported that a person from the Ansar who was called Abu Shu'aib had a slave who was a butcher (by profession). He (Abu Mas'ud) saw Allah's Messenger (ﷺ) and found signs of hunger on his face. He said to the servant: 0 ye, prepare for us food sufficient for five persons, for I intend to invite Allah's Messenger (ﷺ) who would be the fifth amongst the five. He (the narrator) reported that he then prepared the food and came to Allah's Messenger (ﷺ) and invited all the five (including him) who was the fifth amongst them to the feast. A man followed him and when Allah's Messenger (ﷺ) reached the door, he said: This man has followed us; if you like you may permit him (to join the meal) and if you like he can go back. Thereupon the person said: Allah's Messenger (ﷺ) , I permit him.