by Imam Malik, translation by A'isha `Abdarahman at-Tarjumana and Ya`qub Johnson , Volume: Shortening the Prayer
Chapter: The Prayer of a Traveller when Undecided whether to Remain in a Place or Not
Yahya related to me from Malik from Ibn Shihab from Salim ibn Abdullah that Abdullah ibn Umar used to say, "I pray the prayerof a traveller as long as I am undecided whether to remain somewhere or not, even if I am detained for twelve nights."
Yahya related to me from Malik from Nafi that Ibn Umar stayed in Makka for ten nights, shortening the prayer, except when he prayed it behind an imam, in which case he followed the imam's prayer.
9.5 Doing the Full Prayer when One Decides to Remain in a Place