Sayyiduna Kaladah bin al-Hanbal (may Allah be pleased with him) narrates that Safwan bin Umayyah sent him, at the time of the Conquest, with beestings (first milk), a young deer and small cucumbers, while the Prophet (peace and blessings be upon him) was in the upper part of the valley. He said: I went in to him without saying the greeting of peace and without seeking permission, so the Prophet (peace and blessings be upon him) said: "Go back and say: 'As-salamu alaykum (Peace be upon you), may I come in?'" This was after Safwan had accepted Islam.
Amr said: Umayyah bin Safwan also told me this report, but he did not say: I heard it from Kaladah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17666