Narrated `Ikrima: Ibn `Abbas said, "We stayed for 19 days with Prophet on a journey during which we used to offer shortened prayers." Ibn `Abbas added, "We offer the Qasr prayer (i.e. shortened prayer) If we stay up to 19 days as travelers, But if we stay longer, we offer complete prayers.
Hadith Referenceصحيح البخاري / كتاب المغازي / 4299
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة