Silsilat al-Ahadith al-Sahihah

Khalidah bin Khubul says: Safwan bin Umayyah sent me to the Prophet Muhammad (peace be upon him) with milk, a cloak, and small cucumbers. The Prophet (peace be upon him) was in the upper part of the valley. I greeted him and went to him without seeking permission. The Prophet (peace be upon him) said: "Go back and (first) say: As-salamu alaikum, may I come in?"