None but the Muhajirun and the Ansar shall stand in the first row

Qays bin Ubad narrates: I was present in Madinah. When the iqamah was called for the prayer, I went forward and stood in the first row. Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) came out and made his way through the rows to the front. With him came out a man of wheat-brown complexion and a light beard (Sayyiduna Ubayy bin Ka'b). He looked at the faces of the people, and when he saw me, he moved me back and stood in my place. This weighed very heavily on me. When he finished the prayer, he turned towards me and said: "(O young man!) Do not take offence and do not be sad. Did this weigh heavily on you? The fact is that I heard the Messenger of Allah (peace and blessings be upon him) say: 'None should stand in the first row except the Muhajirun and the Ansar.'" I asked: Who is this man? The people said: This is Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him).
This hadith has a sahih (authentic) chain, and al-Hakam bin Abd al-Malik is alone in narrating it from Qatadah.

It is narrated from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A surah has been revealed to me, and I have been commanded to recite it to you." I said: Was I named (by Allah)? He (peace and blessings be upon him) said: "Yes." (The narrator says:) I asked Ubayy bin Ka'b: O Abu al-Mundhir, did this make you happy? He said: What could stop me from being happy when Allah, the Blessed and Exalted, says: "Say: It is by the bounty of Allah and His mercy, so let them rejoice in that." [Surah Yunus: 58]
This hadith has a sahih (authentic) chain, but the two Shaykhs (Bukhari and Muslim) did not record it.

Ikrimah bin Sulayman narrates: I recited the Qur'an to Isma'il bin Abdullah bin Qustantin. When I reached Surah al-Duha, he said to me: Say the takbir (Allahu Akbar) at the end of every surah until you complete the Qur'an, for I recited the Qur'an to Abdullah bin Kathir, and when I reached Surah al-Duha, he said the takbir until the Qur'an was completed. Abdullah bin Kathir said that he had recited to Mujahid and he had given him the same instruction; Mujahid said that Sayyiduna Ibn Abbas (may Allah be pleased with them both) had instructed him to do so; Ibn Abbas (may Allah be pleased with them both) said that Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) had instructed him to do so; and Ubayy bin Ka'b said that the Prophet (peace and blessings be upon him) had instructed him to do so.
This hadith has a sahih (authentic) chain, but the two Shaykhs (Bukhari and Muslim) did not record it.