(2) باب قَصْرِ الصَّلاَةِ بِمِنًى
Salim b. 'Abdullah (b. 'Umar) reported on the authority of his father that Allah's Messenger (ﷺ) observed the prayer of a traveller, i. e. two rak'ahs in Mina, and other places; so did Abu Bakr and 'Umar, and 'Uthman too observed two rak'ahs at the beginning of his caliphate, but he then completed four.
Reference: Sahih Muslim 694 a
In-book reference: Book 6, Hadith 21
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1477