From Sahih Bukhari (Hadith 4129):
Narrated Salih bin Khawwat:Concerning those who witnessed the Fear Prayer that was performed in the battle of Dhat-ur-Riqa' in the company of Allah's Messenger (ﷺ); One batch lined up behind him while another batch (lined up) facing the enemy. The Prophet (ﷺ) led the batch that was with him in one rak`a, and he stayed in the standing posture while that batch completed their (two rak`at) prayer by themselves and went away, lining in the face of the enemy, while the other batch came and he (i.e. the Prophet) offered his remaining rak`a with them, and then, kept on sitting till they completed their prayer by themselves, and he then finished his prayer with Taslim along with them
Reference: Bukhari 4129