(1) باب صَلاَةِ الْمُسَافِرِينَ وَقَصْرِهَا
Musa b. Salama Hudhali said:
I asked Ibn 'Abbas: How should I say prayer when I am in Mecca, and when I do not pray along with the Imam? He said: Two rak'ahs (of prayer) is the Sunnah of Abu'l-Qasim (ﷺ).
Reference: Sahih Muslim 688 a
In-book reference: Book 6, Hadith 8
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1465