Musannaf Ibn Abi Shaybah

Hazrat Kathir bin Aflah says that I reached the mosque, and I had not yet performed the Maghrib prayer. In the meantime, the congregation stood up, and I joined them in prayer, intending it as Maghrib. But I found out that they were actually performing the Isha prayer. So I first performed the Maghrib prayer and then the Isha prayer. Then I asked the elders about this matter, and they instructed me to do exactly what I had done.