Musannaf Ibn Abi Shayba 3:6105

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, who said: Masruq and Jundub caught one rak'ah of the Maghrib prayer. When the Imam performed the taslim, Masruq stood up and added one rak'ah to it, then he sat. Jundub stood up for all of them [the remaining rak'ahs], then he sat at the end of them. This was mentioned to Abdullah, and he said: "Both of them have done well, but doing as Masruq did is more beloved to me."