Sahih al-Bukhari 4299
Sahih al-Bukhari · Book 64: Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi) · The stay of the Prophet (saws) in Makkah
Narrated `Ikrima:
حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ ، حَدَّثَنَا أَبُو شِهَابٍ ، عَنْ عَاصِمٍ ، عَنْ عِكْرِمَةَ ، عَنِ ابْنِ عَبَّاسٍ ، قَالَ أَقَمْنَا مَعَ النَّبِيِّ صلى الله عليه وسلم فِي سَفَرٍ تِسْعَ عَشْرَةَ نَقْصُرُ الصَّلاَةَ. وَقَالَ ابْنُ عَبَّاسٍ وَنَحْنُ نَقْصُرُ مَا بَيْنَنَا وَبَيْنَ تِسْعَ عَشْرَةَ، فَإِذَا زِدْنَا أَتْمَمْنَا .
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.