Read all Ahadith in chapters on seeking permission by jami al tirmizi

Narrated Abu Hurairah: that the Messenger of Allah (ﷺ) said: By the One in Whose Hand is my soul! You will not enter Paradise until you believe, and you will not believe until you love one another. Shall I inform you about a matter which if you do it, then you will love one another? Spread the Salam among each other.

Narrated 'Imran bin Husain: A man came to the Prophet (ﷺ) and said: 'As-Salamu 'Alaykum (Peace be upon you).' [He said:] So the Prophet (ﷺ) said: 'Ten.' Then another came and he said: 'As-Salamu 'Alaykum Wa Rahmatullah (Peace be upon you, and the mercy of Allah).' So the Prophet (ﷺ) said: 'Twenty.' Then another came and said: 'As-Salamu 'Alaykum Wa Rahmatullahi Wa Barakatuh (Peace be upon you, and the mercy of Allah, and His Blessings).' So the Prophet (ﷺ) said: 'Thirty.'

Narrated Abu Sa'eed: Abu Musa sought permission to enter upon 'Umar. He said: 'As-Salamu 'Alaykum (Peace be upon you). May I enter?' 'Umar said: 'Once.' Then he was silent for some time. Then he said: 'As-Salamu 'Alaykum (Peace be upon you). May I enter?' 'Umar said: Twice.' Then he was silent for some time. Then he said: 'As-salamu 'Alaykum (Peace be upon you). May I enter?' 'Umar said: 'Three times.' Then he (Abu Musa) left. 'Umar said to the gate-keeper: 'What did he do?' He replied: 'He left. He said: 'Bring him to me.' So when he came, 'Umar said to him: 'What is this that you have done?' He said: 'The Sunnah.' He said: 'The Sunnah? By Allah! You had better bring me proof or a witness to clarify this, or I will do this or that to you.' He said So he came to us while we were sitting with Ansar. He said: 'O People of the Ansar! Are you not the most knowledgeable people about the Ahadith of the Messenger of Allah (ﷺ)? Did the Messenger of Allah (ﷺ) not say: Seeking permission is to be done three time. Either you are permitted, or other wise leave? The people began joking. Abu Sa'eed said: Then I raised my head toward him and said: Whatever punishment you are afflicted with because of this, then I shall be your partner in it. So he went to 'Umar to inform him him about it, and 'Umar said: I did not know about about this.

Narrated Ibn 'Abbas: that Uman bin Al-Khattab said: I sought permission (to enter) from the Messenger of Allah (ﷺ) three times, then he permitted me.

Narrated Abu Hurairah: A man enter the Masjid and performed Salat while the Messenger of Allah (ﷺ) was sitting at the back of the Masjid. Then he came to greet him, so the Prophet (ﷺ) said: Wa Alaikum (and upon you); go back and pray for indeed you have not prayed.' And he mentioned the Hadith in its entirety.

Narrated Abu Salamah: that 'Aishah narrated to him that he Messenger of Allah (ﷺ) said to her: Indeeed Jibril has sent Salam to you. She said: And upon him be peace and the mercy of Allah and His Blessings.

Narrated Abu Umamah: They said: 'O Messenger of Allah! When two men meet, which of them initiates the Salam?' He said: 'The nearest of them to Allah.'

Narrated 'Amr bin Shu'aib: from his father, from his grandfather, that the Messenger of Allah (ﷺ) said: He is not one of us who resembles other than us, no who resembles the Jews nor the Christians. For indeed greeting of the Jews is pointing the finger, and the greeting of the Christians is waving with the hand.

Narrated Sayyar: I was walking with Thabit Al-Bunani. He passed by some boys, so he said Salam to them. Then Thabit said: 'I was with Anas when he passed by some boys and gave the Salam to them, and Anas said: I was with the Prophet (ﷺ) when he passed by some boys and he gave the Salam to them.'

Narrated Asma bint Yazid: that the Messenger of Allah (ﷺ) passed through the Masjid one day, and a group of women were sitting, so he motioned his hand with the Salam - 'Abdul-Hamid (one of the narrators) gestured with his hand.