Musnad Ahmad 175:11

Ali ibn Ishaq narrated to us, he said: Abdullah informed us, he said: Ma'mar informed us, from al-Zuhri, from Abd al-Rahman ibn Ka'b ibn Malik, from his father, who said: "The Prophet, may Allah bless him and grant him peace, arrived—meaning from Tabuk—and prayed two rak'ahs in the mosque. And he used to do that whenever he arrived from a journey."