Narrated Imran ibn Husayn: I went on an expedition with the Apostle of Allah (peace_be_upon_him), and I was present with him at the conquest. He stayed eighteen days in Mecca and prayed only two rak'ahs (at each time of prayer). And he said: You who live in the town must pray four; we are travellers. [+] [Abu Dawud 002:1225]