Musannaf Ibn Abi Shayba 3:5903

Waki' narrated to us, from Sufyan, from Salim, from Sa'id ibn Jubayr, that the Prophet (peace and blessings of Allah be upon him) prayed two rak'ahs with them. So there were two rak'ahs for the Prophet (peace and blessings of Allah be upon him), and for them, there was one rak'ah [and another] one rak'ah.