A Companion from the Ansar whose kunyah was Abu Shu'ayb said: I came to the Prophet (peace and blessings be upon him) and perceived hunger in his face. I went to a slave of mine who was a butcher and told him to prepare food for five men. Then I invited the Prophet (peace and blessings be upon him). Five people came, including the Prophet (peace and blessings be upon him), and one more person followed them. When they reached the door, he said: "This man has followed us. If you wish, give him permission! Otherwise he will go back." So I gave him permission.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators are the narrators of the Sahih.
Sayyidah Aishah Siddiqah (may Allah be pleased with her) narrates that the Prophet (peace and blessings be upon him) said: "Whoever enters upon a people's food without having been invited enters as a sinner (fasiq) and eats what is unlawful (haram)."
Al-Bazzar recorded it; its chain contains a narrator, Yahya bin Khalid, and he is majhul (unknown). Al-Tabarani also recorded it in al-Mu'jam al-Awsat through the same route; however, in it he recorded these words: "Whoever comes to a people's food to which he was not invited and then eats something has eaten what is unlawful."
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates this as a marfu' hadith: The Prophet (peace and blessings be upon him) said: "Whoever comes to food to which he was not invited enters as a thief and eats what is unlawful (haram)." (Allamah al-Haythami says:) I say:
Abu Dawud recorded this report; however, he did not record these words: "and eats what is unlawful."
Al-Bazzar recorded it; its chain contains a narrator, Aban bin Tariq, and he is da'if (weak).
Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: In the Days of Ignorance (Jahiliyyah) we used to call the person who joined a meal to which he had not been invited an 'imma'ah' (a hanger-on), and among you the imma'ah is the person who puts his religion behind his back.
In another narration from him it is stated: In the Days of Ignorance we used to call an 'imma'ah' the person who had been invited to food and another man followed along behind him; today it is said of the person who puts his religion behind his back for the sake of people. We used to call lying 'samar' (night-talk), and today it is called 'qil wa qal' (idle gossip). Al-Tabarani recorded all of these reports in al-Mu'jam al-Kabir with two chains, and both of them are da'if (weak).