It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him), he says that when a person says: May I come in? and does not say «السلام علیکم» , then say to him: No, you cannot come in until you bring the key. I said: «السلام» ......? He said: Yes.

It is narrated from a man of Banu Amir that he came to the service of the Prophet (peace be upon him) and said: "May I come in?" The Prophet (peace be upon him) said to a slave girl: "Go outside and tell him to seek permission like this: «السلام علیکم» , may I come in? He does not know how to seek permission properly." He says that before the slave girl went out, I heard the words of the Prophet (peace be upon him) and said: «السلام علیکم» , may I come in? The Prophet (peace be upon him) said: "And upon you, come in." I entered and said: "What have you brought (from Allah)?" The Prophet (peace be upon him) said: "I have brought nothing but good for you. I have come to you so that you worship Allah alone with no partner, and abandon the worship of Lat and Uzza, perform five prayers in the day and night, fast for one month in the year, perform Hajj of this House (the Ka'bah), and take wealth from your rich and give it to your poor." He says: I asked: "Is there any knowledge from among the knowledge that you do not know?" The Prophet (peace be upon him) said: "Allah alone has granted the knowledge of good, and there are many matters of knowledge that none knows except Allah. Five things are such that none knows except Allah." Then he recited this verse: «إِنَّ اللَّهَ عِنْدَهُ عِلْمُ السَّاعَةِ وَيُنَزِّلُ الْغَيْثَ وَيَعْلَمُ مَا فِي الْأَرْحَامِ وَمَا تَدْرِي نَفْسٌ مَاذَا تَكْسِبُ غَدًا وَمَا تَدْرِي نَفْسٌ بِأَيِّ أَرْضٍ تَمُوتُ» [سورہ لقمان: 34] "With Allah alone is the knowledge of the Hour, He sends down the rain, He knows what is in the wombs. No person knows what he will earn tomorrow, and no person knows in which land he will die."