Abu Dawud
Prayer
Book Number: 002 / Hadith Number: 1226
Narated By Abdullah ibn Abbas : The Apostle of Allah (pbuh) had a stop of seventeen days in Mecca and he shortened the prayer (i.e. prayed two rak'ahs at each time of prayer). Ibn Abbas said: He who stays seventeen days should shorten the prayer; and who stays more than that should offer complete prayer.