The Prophet ﷺ said, "A man's messenger sent to another man serves as his permission to enter."
عن النبي ﷺ قال: رسول الرجل إلى الرجل إذنه.
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Abu Dawud (5189) and Bukhari in Adab al-Mufrad (1076) both narrated it from Musa bin Ismail, who said, Hammad bin Salama narrated to us, from Habib and Hisham, from Muhammad, from Abu Hurairah, and he mentioned it. Its isnad is sahih. Muhammad here is Ibn Sirin, and Habib is Habib bin Shahid.As for what has been narrated from Abu Hurairah that the Messenger of Allah ﷺ said, "If one of you is invited to a meal and comes along with the messenger, that itself counts as permission for him," this is disconnected. Abu Dawud (5190) and Bukhari in Adab al-Mufrad (1075) both narrated it through the report of Abdul-Ala, who said, Saeed narrated to us, from Qatada, from Abu Rafi, from Abu Hurairah, and he mentioned it.Abu Ali Lului said, "I heard Abu Dawud say, 'Qatada never heard anything directly from Abu Rafi.'"I say that Imam Ahmad said that Hasan and Khilas come in between Qatada and Abu Rafi. Abu Rafi is Nufay of Basra, the goldsmith. Moreover, Qatada was known to conceal gaps in his chains of transmission, and since he did not explicitly state that he heard this directly, it appears that he concealed a gap in this hadith as well.