It goes along the lines of what is mentioned in a lecture and on the internet, which is not the Hadith mentioned in Sahih Muslim (190a), but is still somehow similar to this following narration (if it is true):
The story: The Prophet (ﷺ) laughed one day and so his Sahabah asked: "What are you smiling about?" He said: "I was looking into the Day of Judgment" - and every time the Prophet (ﷺ) saw the Day of Judgement, he would (usually) cry or panic and worry for everyone. But this time, he smiled and he said: "I smiled because the People, on the Day of Judgment, a group of them will laugh", they asked: "Who are 'they'" and he said: "They are People on the Judgement Day who will laugh", and the Sahabah asked: "Who are they?" The Prophet (ﷺ) said: "They are people who committed sins and they will laugh on the Day of Judgement [...] and the people will ask them what they were laughing about. They will say: "We've sinned [...] and we repented [...] and our sins became good deeds!"
This is the only video that I could find which is refering to this narration, but it is not revealing a reference or its authenticity.