Musannaf Ibn Abi Shaybah

Hazrat Wabra bin Abdur Rahman narrates that I, Ibrahim Nakha'i, and Hazrat Abdur Rahman bin Aswad performed the Maghrib prayer. Then we came towards the mosque and saw that people were still performing the Maghrib prayer. We also joined them in congregation. When the Imam finished the prayer with salam, Abdur Rahman bin Aswad and I became doubtful about what to do next, while Ibrahim added one rak'ah with them.