Sunan an Nasai
867
Sahih+2

It was narrated that Ibn Buhainah said:"The Iqamah for Subh prayer was said, and the Messenger of Allah (ﷺ) saw a man praying while the Mu'adhdhin saying the Iqamah. He said: 'Are you praying Subh with four Rak'ahs?

SahihAbu Ghuddah
SahihAl-Albani