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."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / Q13412