The story of Uwais Al-Qarni was mentioned in Sahih Muslim as well as in other books. Now even though he was from the Taabi'een and did not see the Messenger [Sallah Allahu 'Alaihi wa salam], the Messenger [Sallah Allahu 'Alaihi wa salam] had advised 'Umar ibn Al-Khatab [Radiya Allahu 'Anhu] that if he meets [Uwais] then he, 'Umar, should ask [Uwais] to ask Allah to forgive him and to make supplication for him.
Asir ibn Jaabir radhiallahu 'anhu narrated:
Whenever people would come from Yemen, 'Umar radhiallahu 'anhu would ask them, "Is Uways Al-Qaranee amongst you?" until, one year, he met Uways.
He said, "Are you Uways Al-Qaranee?" He said, "Yes."
'Umar continued, "From Muraad, then Qaran?" He said, "Yes."
'Umar then asked, "Were you once afflicted with leprosy and your skin healed except for a dirham's area?" Uways said, "Yes."
'Umar finally asked, "Do you have a mother (that is alive)?" He said, "Yes."
'Umar then said, "I heard the Messenger of Allah – sallallahu 'alayhi wa sallam – say, 'Uways ibn Aamir will come to you with the delegations from Yemen, from Muraad, then from Qaran. He was once afflicted with leprosy and his skin healed except for a dirham's area. He has a mother, and he treats her kindly. If he was to ever swear by Allah (for something) Allah would fulfill his oath. If you can, request that he ask forgiveness for you."
'Umar then requested from Uways, "Ask forgiveness for me." And Uways Al-Qaranee did. (Sahih Muslim)
Recommended further reading: I met Uwais Al Qarni.