Sunan Abi Dawud Book 2, Hadith 186
I said the morning prayer along with the prophet (ﷺ) at Mina. He narrated the rest of the tradition to the same effect.
Yazid prayed along with the Messenger of Allah (ﷺ) when he was a young boy. When he (the Prophet) had prayed there were two persons (sitting) in the corner of the mosque; they did not pray (along with the Prophet). He called for them. They were brought trembling (before him). He asked: What prevented you from praying along with us? They replied: We have already prayed in our houses. He said: Do not do so. If any of you prays in his house and finds that the imam has not prayed, he should pray along with him; and that will be a supererogatory prayer for him.
I came while the Prophet (ﷺ) was saying the prayer. I sat down and did not pray along with them. The Messenger of Allah (ﷺ) turned towards us and saw that Yazid was sitting there. He said: Did you not embrace Islam, Yazid? He replied: Why not, Messenger of Allah; I have embraced Islam. He said: What prevented you from saying prayer along with the people? He replied: I have already prayed in my house, and I thought that you had prayed (in congregation). He said: When you come to pray (in the mosque) and find the people praying, then you should pray along with them, though you have already prayed. This will be a supererogatory prayer for you and that will be counted as obligatory.