Hamzahbin Mughirah bin Shu'bah narrated that his father said:
"TheMessenger of Allah (ﷺ) lagged behind (on a journey) and we reachedthe people when 'Abdur Rahman bin 'Awf had already led them inoneRak'ah of the prayer. When he realized that the Prophet (ﷺ)wasthere, he wanted to step back, but the Prophet (ﷺ) gestured tohimthat he should complete the prayer. He said: 'You have donewell, dothe same in the future.'"
English reference: Vol. 1, Book 5, Hadith 1236
Arabic reference: Book 5, Hadith 1294