Sunan Abi Dawud Book 5, Hadith 16
A man came while the Prophet (ﷺ) was leading the people in the dawn prayer. He prayed the two rak'ahs and then joined the congregational prayer led by the Prophet (ﷺ). When he finished the prayer, the Prophet (ﷺ) said: So-and-so, which was your real prayer, the one you prayed alone or the one offered with us ?
I came out with the Prophet (ﷺ) to offer the dawn prayer. When he passed by a sleeping man he called him for prayer or moved him with his foot. The narrator Ziyad said: This tradition has been reported to us by AbulFadl.
The Messenger of Allah (ﷺ)as saying: When the iqamah is pronounced for prayer, no prayer is valid except the obligatory prayer.