(1) باب صَلاَةِ الْمُسَافِرِينَ وَقَصْرِهَا
Ibn 'Abbas reported:
Allah has prescribed the prayer through the word of your Prophet (ﷺ) as four rak'ahs when resident, two when travelling, and one when danger is present. (ES)
Reference (ES): Sahih Muslim 687 a (ES)
In-book reference (ES): Book 6, Hadith 6 (ES)
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1463 (ES)