Musannaf Ibn Abi Shayba 3:5825

Waki’ narrated to us, he said: Al-Muthanna bin Sa’id narrated to us, from Abu Jamra Nasr bin ‘Imran, who said: I said to Ibn ‘Abbas: "We prolong our stay during military expeditions in Khurasan, so what is your opinion?" He said: "Pray two rak'ahs, even if you stay for ten years."