The Prophet (ﷺ) said, "It is not lawful for a Muslim to desert (not to speak to) his brother Muslim for more than three days while meeting, one turns his face to one side and the other turns his face to the other side. Lo! The better of the two is the one who starts greeting the other."
Sahih al-Bukhari Book 79, Hadith 11
← Previous Hadith A man asked the Prophet, "What Islamic traits are the best?" The Prophet said, "Feed the people, and greet those whom you know and those whom you do not know."

Sahih al-Bukhari Book 79, Hadith 10 Next Hadith → that he was a boy of ten at the time when the Prophet (ﷺ) emigrated to Medina. He added: I served Allah's Apostle for ten years (the last part of his life time) and I know more than the people about the occasion whereupon the order of Al-Hijab was revealed (to the Prophet). Ubai b n Ka`b used to ask me about it. It was revealed (for the first time) during the marriage of Allah's Messenger (ﷺ) with Zainab bint Jahsh. In the morning, the Prophet (ﷺ) was a bride-groom of her and he Invited the people, who took their meals and went away, but a group of them remained with Allah's Messenger (ﷺ) and they prolonged their stay. Allah's Messenger (ﷺ) got up and went out, and I too, went out along with him till he came to the lintel of `Aisha's dwelling place. Allah's Messenger (ﷺ) thought that those people had left by then, so he returned, and I too, returned with him till he entered upon Zainab and found that they were still sitting there and had not yet gone. The Prophet (ﷺ) went out again, and so did I with him till he reached the lintel of `Aisha's dwelling place, and then he thought that those people must have left by then, so he returned, and so did I with him, and found those people had gone. At that time the Divine Verse of Al-Hijab was revealed, and the Prophet (ﷺ) set a screen between me and him (his family).

Sahih al-Bukhari Book 79, Hadith 12