As Uways ibn ‘Aamir ibn Juz’ ibn Maalik al-Qarni al-Muraadi al-Yamaani أويس بن عامر بن جزء بن مالك القرني المرادي اليماني (short Uwais al-Qarni) accepted Islam during the time of the prophet (), but never met him therefore he is considered among the tabi'in and is not a sahabi. What prevented him from travelling to meet him was the fact that he was preoccupied with taking care of his mother, as was narrated by Abu Nu'aym in Hilyat al-Awliya'.
It was mentioned that 'Omar ibn al-Khattab () whenever a caravan or tarvellers from Yemen came to Medina used to ask: "Is there amongst you Uwais ibn 'Aamir?". So the prophet () has reported to his companions about this man and described him.
This was compilled by Muslim in his Sahih:
Usair b. Jabir reported that when people from Yemen came to help (the Muslim army at the time of jihad) he asked them:
Is there amongst you Uwais b. 'Amir? (He continued finding him out) until he met Uwais.
He said: Are you Uwais b., Amir? He said: Yes. He said: Are you from the tribe of Qaran? He said: Yes. He (Hadrat) 'Umar (again) said: Did you suffer from leprosy and then you were cured from it but for the space of a dirham? He said: Yes. He ('Umar) said: Is your mother (living)? He said: Yes. He ('Umar) said: I heard Allah's Messenger (ﷺ) say: There would come to you Uwais b. Amir with the reinforcement from the people of Yemen. (He would be) from Qaran, (the branch) of Murid. He had been suffering from leprosy from which he was cured but for a spot of a dirham. His treatment with his mother would have been excellent. If he were to take an oath in the name of Allah, He would honour that. And if it is possible for you, then do ask him to beg forgiveness for you (from your Lord). So he (Uwais) begged forgiveness for him. Umar said: Where do you intend to go? He said: To Kufa. He ('Umar) said: Let me write a letter for you to its governor, whereupon he (Uwais) said: I love to live amongst the poor people. When it was the next year, a person from among the elite (of Kufa) performed Hajj and he met Umar. He asked him about Uwais. He said: I left him in a state with meagre means of sustenance. (Thereupon) Umar said: I heard Allah's Messenger (ﷺ) as saying: There would come to you Uwais b. 'Amir, of Qaran, a branch (of the tribe) of Murid, along with the reinforcement of the people of Yemen. He had been suffering from leprosy which would have been cured but for the space of a dirham. His treatment with his mother would have been very kind. If he would take an oath in the name of Allah (for something) He would honour it. Ask him to beg forgiveness for you (from Allah) in case it is possible for you. So he came to Uwais and said.: Beg forgiveness (from Allah) for me. He (Uwais) said: You have just come from a sacred journey (Hajj) ; you, therefore, ask forgiveness for me. He (the person who had performed Hajj) said: Ask forgiveness for me (from Allah). He (Uwais again) said: You have just come from the sacred journey, so you ask forgiveness for me. (Uwais further) said: Did you meet Umar? He said: Yes. He (Uwais) then begged forgiveness for him (from Allah). So the people came to know about (the status of religious piety) of Uwais. He went away (from that place). Usair said: His clothing consisted of a mantle, and whosoever saw him said: From where did Uwais get this mantle? (Sahih Muslim)
beside this there's a hadith that actually confirms that he is a tabi'y:
I heard Allah's Messenger (ﷺ) as saying: Worthy amongst the successors would be a person who would be called Uwais. He would have his mother (living with him) and he would have (a small) sign of leprosy. Ask him to beg pardon for you (from Allah). (Sahih Muslim)
For further information refer to this article and this fatwa islamqa #125276 with his biography. As he is said to have died during the battle of Siffin on the side of 'Ali ibn abi Talib () you may find here -in Arabic- some Shi'a references telling about him.