Abdur Rahman bin Abi Layla عبد الرحمن بن أبي ليلى · The Book on Traveling

"I prayed with the Prophet both, while a resident and while traveling. So I prayed four for Zuhr with him as a resident, and two Rak'ah after it. I prayed two Rak'ah for Zuhr with him while traveling and two Rak'ah after it, and two Rak'ah for Asr, and he did not pray anything after it. Maghrib while a resident and traveling is the same; three Rak'ah, it is not decreased as a resident nor while traveling. It is Witr…

the Messenger of Allah said: "When one of you comes to the Salat and (finds) the Imam is in a position, then do as the Imam is doing."