Abu al-Abbas said: "And he (peace and blessings be upon him) forbade arriving unexpectedly at a meal (without an invitation); and Sayyiduna Abu al-Darda' (may Allah be pleased with him) arrived unexpectedly at his (peace and blessings be upon him) meal, and he (peace and blessings be upon him) ordered him to eat; and this was particular to him (peace and blessings be upon him)."
The Shaykh (Imam al-Bayhaqi) (may Allah have mercy on him) said: "I do not know the hadith forbidding arriving unexpectedly at a meal in this form through any chain the like of which is established; what I know is among the reports that carry part of its meaning."
Abdullah bin Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) said: "Whoever is invited and does not accept has disobeyed Allah and the Messenger, and whoever enters without an invitation enters as a thief and leaves as a raider."
This was said concerning a man who goes in to another, knowing that he is eating, in order to eat with him. And a hadith has been narrated that negates the special exemption that Abu al-Abbas imagined regarding the meal of the Prophet (peace and blessings be upon him) in the story of Abu al-Darda'.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13412